Audio Precision BT3 Acoustic Analyzer User Manual
- June 16, 2024
- Audio Precision
Table of Contents
User Manual
Bluetooth I/O
Introduction
The APx Bluetooth Duo option is a hardware module available for the APx
modular analyzers (the APx555, and the APx525 and 585 families of analyz-ers,
including the APx582 and the APx516). It provides Bluetooth wire-less
technology source and sink interfaces.
The APx Bluetooth profiles support audio in a lowerquality (voice) mode (the
HFP and HSP profiles) and in a higher-quality (music) mode (the A2DP profile).
This chapter discusses operation of the Bluetooth Duo option.APx500 version
4.5 supports the Bluetooth Duo option, and also provides support for the
legacy Bluetooth modules. Operation of the legacy Bluetooth modules is
discussed.
Identification
The most obvious difference between the legacy Bluetooth modules and the
Bluetooth Duo module is the number of external antennas: the legacy modules
have one; Bluetooth Duo has two.
The Bluetooth Duo module carries the model number 229, and is identified in
the Help > About product components list as Bluetooth Duo Module.
The Bluetooth Monitor
The status of a number of current Bluetooth settings is shown in the Bluetooth
Monitor. Additionally, Bluetooth actions, settings and utility functions are
available through a context menu (right-click in the Bluetooth Monitor
display.) See Bluetooth Monitor
Bluetooth Discovery, Pairing and Connection
Bluetooth connections require successful radio frequency (RF) communication
between the APx analyzer and the DUT, and successful device handshaking
through device discoverability, pairing and connection protocols. Data
transfer is encrypted and must be authorized by the exchange of link keys, and
personal identification number (PIN) codes may be required.
Bluetooth Settings are Global
Bluetooth settings are unique in APx500, in that they are global. This means
the settings made in the Bluetooth Settings dialog affect the entire project:
all measurements, all signal paths.
Source, Sink, Output and Input
When the APx Output Configuration is set to Bluetooth, the instrument can
transmit audio using the A2DP Source profile, the HFP Audio Gateway profile,
or the HSP Audio Gateway profile. When the APx Input Configuration is set to
Bluetooth input, the instrument can receive audio using the A2DP Sink profile,
the HFP Hands Free profile, or the HSP Headset profile.
There is one case where you are allowed to output audio and input audio
simultaneously: Set the APx Profile to A2DP Sink, HFP Hand Free AVRCP
Controller. Connect to the DUT using the HFP Profile. Since HFP is a bi-
directional link, you can both send and receive audio.
Output Configuration: Bluetooth
This Signal Path Setup I/O selection enables output of audio from the APx
generator to a Bluetooth device under test, using Bluetooth radio frequency
(RF) transmission.
Note: The Bluetooth choice is only available for analyzers fitted with
the APx Bluetooth Option module.
Connector
Choose Bluetooth here. Since the Bluetooth connection isn’t valid until you
choose, pair and connect with a device, the Bluetooth Settings dialog opens
immediately.
See page 132.
Settings
Click the Settings… button to discover, select, pair, connect and otherwise
configure a Bluetooth link. See page 132.
Friendly Name
The friendly name of the APx Bluetooth module’s source chip will appear here.
Address
The address of the APx Bluetooth module’s source chip will appear here.
A2DP
The codec settings for the A2DP profile can be viewed and edited here.
Audio Profile
This displays the active profile, if any. See More About Supported Bluetooth
Profiles on page 141.
Connect
If the APx is already paired with one or more Bluetooth devices, you can open
the Connect flyout menu to select a device and one or more profiles for
connec-tion. See More About Supported Bluetooth Profiles on page 141.
Disconnect
If the APx is already connected to a Bluetooth device, you can click the
Disconnect button to terminate the connection.
Actions
Click Actions to open the Bluetooth Actions dialog. If the APx is already
connected to a Bluetooth device, you can initiate Bluetooth Actions from this
dialog.
Only the actions appropriate to the current connection and profile are shown.
See Actions on page 139.
Input Configuration: Bluetooth
This selection enables input of audio from a Bluetooth device under test,
using Bluetooth radio fre-quency (RF) transmission.
Note: The Bluetooth choice is only available for analyzers fitted with
the APx Bluetooth Option module.
Loopback
Loopback is not available when either the Output or Input Configuration is set
to Bluetooth.
Connector
Choose Bluetooth here. Since the Bluetooth connection isn’t valid until you
choose, pair and connect with a device, the Bluetooth Settings dialog opens
immediately.
See page 132.
Settings
Click the Settings… button to discover, select, pair, connect and otherwise
configure a link with a Bluetooth device. See page 132.
Edit Channel Labels
In the Channel Labels dialog you can rename the input channels with names of
your choice. See page 56. These settings are project-wide, but can be
overridden for any measurement result.
To set project colors, click the Project Colors… button in the Labels dialog,
or go to the Project/Sequence Properties dialog, Colors tab. See Setting Graph
Colors and Styles on page 30.
Channels
This is a reading field that displays the current input channel count,
determined by profile settings.
Friendly Name
The friendly name of the APx Bluetooth module’s sink chip will appear here.
Address
The address of the APx Bluetooth module’s sink chip will appear here.
A2DP
The codec settings for the A2DP profile can be viewed and edited here.
Audio Profile
This displays the active profile, if any. See More About Supported Bluetooth
Profiles on page 141.
Connect
If the APx is already paired with one or more Bluetooth devices, you can open
the Connect flyout menu to select a device and one or more profiles for
connection. See More About Supported Bluetooth Profiles on page 141.
Disconnect
If the APx is already connected to a Bluetooth device, you can click the
Disconnect button to terminate the connection.
Actions
Click Actions to open the Bluetooth Actions dialog. If the APx is already
connected to a Bluetooth device, you can initiate Bluetooth Actions from this
dialog.
Only the actions appropriate to the current connection and profile are shown.
See Actions on page 139.
Operation with absent or corrupt interface signal
When Input Configuration is set to a digital input and no signal is present,
or if the signal is corrupt or out of range, the input receiver cannot lock
(synchronize) to the interface signal, and no valid audio can be recovered.
The sample rate indicator in the Status Bar will display an “unlocked”
warning, and any measurement result referencing audio from the unlocked input
will display an “—-” (invalid) result. See page 632 for more about invalid
results.
Bluetooth settings dialog for Bluetooth Duo
Bluetooth Settings dialog for Bluetooth Duo, shown in the A2DP
Source, HFP Audio Gateway, AVRCP Target profile set.
This topic explores Bluetooth Duo settings dialog. The legacy Bluetooth
settings dialog is discussed beginning on page 148.
This dialog provides settings for Bluetooth discovery, pairing, connection and
other configuration. Unlike most APx settings, Bluetooth profile selection,
pairing and connection settings are global to the APx project.
Settings made here affect both Bluetooth source and sink configurations across
all signal paths in the project.
A flow chart depicting discovery, pairing and connection paths is shown on
page 139.
APx Profile Set
APx has four sets of profiles that the Bluetooth Option module can assume.
Each set lists the profiles avail- able for connection and/or the profiles
available for access by a remote device. Choose an APx Bluetooth
Profile Set here.
- A2DP Source, HFP Audio Gateway, AVRCP Target
- A2DP Source, HSP Audio Gateway, AVRCP Target
- A2DP Sink, HFP Hands Free, AVRCP Controller
- A2DP Sink, HSP Headset, AVRCP Controller
In A2DP Source, the APx Bluetooth transmitter mutes the audio when the average
signal level falls below –54 dBFS for more than 1 second. We recommend
maintaining test levels above –54 dBFS for meaning-ful results.
Check for Firmware Updates at Application Start
The Bluetooth Duo hardware module can update its firmware in the field, using
update files that are included with the APx500 software distribution. See
Update Bluetooth Firmware on page 135.
APx Identification
The upper left side of the dialog displays a number of APx Identification
settings readable by other Bluetooth devices.
Friendly Name
The friendly name of the APx Bluetooth module’s Source or Sink chip is
displayed here.
Address
The Address of the APx Bluetooth Source or Sink chip is displayed here.
APx PIN
The APx Bluetooth PIN is displayed here.
Device Class
-
Auto
Auto uses the Device Class assigned by default: for the Source chip, 60020C; for the Sink chip, 240408. -
Custom
Custom allows you to select a Device Class for the active APx Bluetooth chip. Use the browse button to open the Edit Device Class Dialog (page 137).
Discovery
Auto Discoverable/Pair/Connect
When this is selected (the default), the APx Bluetooth Option is discoverable
by remote Bluetooth devices. If the remote device initiates pairing, the APx
will pair. If the remote device initiates connection, the APx is available to
connect for the profiles checked here.
Not Discoverable, No Pair/Connect
When this is selected, the APx Bluetooth Option is not discoverable by remote
devices, and it will not respond to pairing or connection initiated by remote
device.
SSP Mode
APx provides four SSP (Secure Simple Pairing) options.
The Just Works choice is used in Bluetooth device relationships that require
little security. The Numeric Comparison choices are man-in-the-middle (MITM)
interactions for device relationships that require higher security. Choose the
SSP Mode that is appropriate for the Bluetooth device you are testing. See
More About Secure Simple Pairing on page 142 for detailed information.
- Just Works
- Numeric Comparison, Display Only
- Numeric Comparison, Display+Buttons
- Numeric Comparison, Keyboard
Transmit Power
You can choose one of eight RF output transmission power levels between –20
dBm and +8 dBm. The default is +4 dBm.
Active Bluetooth Connection
If Maintain Active Connection is checked, the APx Bluetooth Option will remain
connected to the Bluetooth device under test throughout the project, even
across Signal Paths. However, if you change to Bench Mode, the Bluetooth
device will be disconnected.
Profile Configurations
The upper right side of the dialog displays a number of APx profile
configurations. The controls and settings here vary with Source or Sink
(Target or Controller) settings.
Profile Configurations for Sink/Controller settings
HFP/HSP Profile
If this box is checked, the HFP/HSP profile is enabled. You may elect to use
the profile at connection time, or not. If this box is unchecked, the HFP/ HSP
profile will not be available on the connection menu. These further options
are available:
- Auto Answer Incoming HFP/HSP Calls
- Wideband Speech (mSBC) Enabled
A2DP Profile (when APx Profile is set to Source)
If this box is checked, the A2DP profile is enabled for Source. You may elect
to use the profile at connection time, or not. If this box is unchecked, the
A2DP profile will not be available on the connection menu. These further
options are available:
Codec Settings…
This button opens the A2DP Codec Settings dialog.
A/V Sync Delay
Enter A/V Sync Delay into DUT Delay. See page 136.
A2DP Profile (when APx Profile is set to Sink)
If this box is checked, the A2DP profile is enabled for Sink. You may elect to
use the profile at connection time, or not. If this box is unchecked, the A2DP
profile will not be available on the connection menu. These further options
are available:
Codec Settings…
This button opens the A2DP Codec Settings dialog. See page 135.
Clock Recovery
Clock Recovery enables or disables the sink clock recovery algorithm. See page
136.
-
Fixed
Fixed (the default) sets the A2DP sink sample rate to the negotiated rate. -
(Auto)
Auto enables the A2DP sink clock recovery algorithm.
Report A/V Sync Delay
Report A/V Sync Delay to the connected Source device. See page 136. -
(Auto) (the default)
Auto reports the APx Bluetooth Sink chip A/V Sync Delay. -
Custom
Custom allows you to enter an arbitrary A/V Sync Delay value to be reported.
AVRCP Profile (when APx Profile is set to Target)
If this box is checked, the AVRCP profile is enabled for Target. You may elect
to use the profile at connection time, or not. If this box is unchecked, the
AVRCP profile will not be available on the connection menu. The latest AVRCP
supported by APx is version 1.4. As an alternative, you may choose AVRCP
version 1.0 here.
These further options are available:
Playback Status
See page 137.
Absolute Volume (Remote)
See page 137.
Commands Change Generator Settings. See page 138.
AVRCP Profile (when APx Profile is set to Controller)
If this box is checked, the AVRCP profile is enabled for Controller. You may
elect to use the profile at connection time, or not. If this box is unchecked,
the AVRCP profile will not be available on the connection menu. The latest
AVRCP supported by APx is version 1.4. As an alternative, you may choose AVRCP
version 1.0 here.
These further options are available:
Playback Status
See page 137.
Absolute Volume (Local)
See page 137.
Scan
The lower left area of the dialog has controls and settings to scan for nearby
Bluetooth devices.
Scan for Devices
This button initiates a scan to identify all the discover able Bluetooth
devices within range. Discovered devices are listed in the Current Devices
List.
Scan Duration
This setting limits the scan time to the value set. The maximum time is 48
seconds. The default is 10 seconds.
Get Friendly Names
By default, APx asks for a device’s friendly name. In automated processes,
this process adds extra time.
Uncheck this checkbox to disable this feature.
Filter Devices From Scan
You can filter the scan so only a certain Bluetooth Device Class will be
shown. Click the browse button to open the Edit Device Class dialog.
Device Class
You can select a Device Class as a filter for the scan.
Use the browse button to open the Edit Device Class Dialog (page 137).
Max Devices
You can limit the number of devices found in the filtered scan here. The
default is 10 devices.
Current Devices List
The Current Devices List occupies most of the lower part of the dialog.
This grid shows the devices discovered in the scan, along with information
fields. There are controls to pair, unpair, connect, disconnect, initiate
actions and to copy the device Bluetooth address and link key.
Select a device to configure the relationship.
Clear Devices
You can choose to remove all devices from the list, or all paired devices, or
all unpaired devices. When a device is removed from the list, any pairing
information for that device is also removed. Click Scan to repopulate the
list.
Pair
Pairing provides a way for devices to exchange link keys. To pair with a
device, refer to the documentation received with the device. To enable
pairing, you will typically be required to execute a command or series of
commands at the device. When pairing is enabled, select the device in the
Current Devices List, and click Pair. A Pair Bluetooth Device dialog box will
open.
Some devices may require the exchange of a PIN code. The APx
Bluetooth PIN code is set to 0000; a field in the pairing dialog allows input
of a remote device’s PIN code.
Pairing information is saved in the project, until the Current Devices List is
cleared, or the until device is Unpaired.
Unpair
Unpairs the selected, previously paired device.
Connect
Connects to the selected, previously paired device. A Connect menu opens.
Select the profile you would like to offer to the device. Disconnect
Disconnects the selected, connected device.
Actions
Opens various Actions dialogs. This duplicates the function of the Actions
button shown on Signal Path Setup, without the necessity of leaving the
Bluetooth Settings dialog. See page 139.
Copy
Copies the device address and key link to the Win-dows Clipboard. This text
can then be pasted into another application or tool.
Update Bluetooth Firmware
The Bluetooth Duo hardware module can update its firmware in the field, using
update files that are included with the APx500 software distribution.
If Check for Firmware Updates at Application Start (located at the top of the
Bluetooth Settings panel) is checked, each time the APx500 application is
launched it will check to verify that the Bluetooth firm-ware is correct for
the APx500 version. If the firmware requires updating, the update will begin
immediately and a progress dialog will be displayed. The update may take a few
minutes.
If Check for Firmware Updates at Application Start is unchecked, the APx500
application will not check for updates at launch. Instead, it will check for
updates if and when Bluetooth is selected as an Input or Output. At that time,
the update may take a few minutes.
If the Bluetooth firmware is the correct version for the APx500 software, you
will not be prompted to update.
Codec Settings
A2DP Codec Settings
The Bluetooth A2DP profile always supports the SBC audio codec. Additional
codecs are optional.
In APx, you can select which optional codecs you would like to support, and
edit features of the codecs you choose.
Using the arrow icons at the top of the dialog, you can set an order of
priority. APx will move from the topmost codec downward until finding the
codec that the DUT supports. Codecs supported, in default order of priority:
aptX HD
You can choose to support either or both of the following sample rates for the
aptX HD codec:
- 48 kHz
- 44.1 kHz
aptX Low Latency
You can choose to support either or both of the follow- ing sample rates for
the aptX Low Latency codec:
- 48 kHz
- 44.1 kHz
aptX
You can choose to support any or all of the following sample rates for the
aptX codec:
APx as A2DP source:
-
48 kHz
-
44.1 kHz
-
32 kHz
-
16 kHz
APx as A2DP sink: -
48 kHz
-
44.1 kHz
-
32 kHz
-
16 kHz
AAC
The AAC codec is fixed at MPEG-2/4, AAC-LC, 44.1 kHz, 2 channels.
By default, variable bit rate (VBR) is set. You can dese-lect variable bit
rate to enforce fixed bit rate.
SBC
You can choose to support any or all of the following sample rates for the SBC
codec:
APx as A2DP source:
-
48 kHz
-
44.1 kHz
-
32 kHz
-
16 kHz
APx as A2DP sink: -
48 kHz
-
44.1 kHz
-
32 kHz
-
16 kHz
Additionally, you can choose to support any or all of the following channel modes:
- Joint Stereo
- Stereo
- Dual Channel
- Mono
Clock Recovery
Bluetooth A2DP Sink Clock Recovery
Clock Recovery: Fixed (the default) does not attempt to algorithmically
correct transmission errors, but sets the A2DP sink sample rate at the
negotiated rate. This provides stable frequency measurements, but may
occasionally be subject to glitches due to packet loss or buffer overruns.
Generally, we recommend using the Fixed setting, particularly when using the
aptX Low Latency codec.
Clock Recovery: (Auto) engages an A2DP sink algorithm that compensates for RF
packet loss or sample rate drift between source and sink. Ideally, this
compensation is unnoticed by the listener, providing a pleasant listening
experience; it will, however, create small but measurable sample rate and
audio frequency variations.
A/V Sync Delay
A/V Sync Delay
AV Sync Delay features are not supported by the Legacy Bluetooth Option.
This feature of A2DP allows the sink device to notify the source device of any
rendering delay, enabling the source device to compensate for the delay.
For example, a source device may provide video to a television monitor via a
hard-wired connection, but route the audio through a Bluetooth A2DP connection
to speakers or headphones. Any delay in the audio path will cause the audio to
lag the video. If the source device is informed of the rendering delay in the
sink device, it can delay the video stream by that amount and maintain proper
synchronization between video and audio.
A2DP Source
When A2DP Source is selected, you can choose Enter A/V Sync Delay into DUT
Delay to apply the delay reported by the remote sink device to the APx DUT
Delay feature.
The delay value entered into DUT Delay is updated each time the remote device
reports a new delay value.
The Bluetooth Monitor will indicate the delay reported from the remote sink
device. If the remote device does not support this feature, the monitor entry
will read “N/A”.
A2DP Sink
When A2DP Sink is selected, APx provides an A/V Sync Delay value for the
remote device to read.
For Report A/V Sync Delay you can choose either
-
(Auto)
Auto reports the current delay in the Bluetooth chip internal to the APx, which will vary with configuration and connection.
or -
Custom
Custom allows you to enter an arbitrary delay value for the remote source device to read. The range is 100 ns to 1.6 s.
Edit Device Class
This dialog will generate a Bluetooth Device Class hex code from your
selections.
Choose one or more Major Service Class(es), a
Major Device Class, and a Minor Device Class (if available.) This dialog will
also identify a Device Class if you type a valid hex code in the Device Class
field, and press the Enter key on the PC keyboard.
APx Device Class
If you have come to this dialog from the APx Custom Device Class setting,
click OK to enter the code generated here as the APx Custom Device Class,
which will be asserted in both Source and Sink profiles.
Scan Filter Device Class
If you have come to this dialog from the Filter Devices From Scan setting,
click OK to enter the code generated here as the scan filter Device Class.
Note: this feature is not supported by the
Legacy Bluetooth Option.
AVRCP Playback Status
AVRCP Playback Status features are not supported by the Legacy Bluetooth
Option.
Playback Status is a feature introduced in AVRCP 1.3.
This feature is intended to allow devices such as car kits to ask a phone
whether a song is playing or not.
This prevents certain “out of band” audio noises from the user, such as key
presses while dialing a phone number. The car kit will suppress audio from the
A2DP source device (which is also the AVRCP target) when the play status is
not PLAYING.
AVRCP Controller profile
In the AVRCP Controller profile, APx acts as a A2DP rendering device (a sink
such as a speaker or headphone), receiving an audio stream from a remote media
player such as a phone. APx uses AVRCP Commands to control the remote media
player.
When the AVRCP Controller profile is selected, the Playback Status Event
checkbox on the Bluetooth Settings panel allows you to enable or disable
Playback Status.
This setting is enabled by default. Toggling this setting will disconnect any
active connection.
When the AVRCP Controller profile is selected, and Playback Status Event is
enabled, and the connected AVRCP Target device supports this notification, the
Play Status is indicated in the Bluetooth Monitor. If the connected AVRCP
Target device does not support it, the Bluetooth Monitor should indicate
“N/A”.
AVRCP Target profile
In the AVRCP Target profile, APx acts as an A2DP source device, sending an
audio stream to a remote rendering device (speaker or headphones). APx
responds to AVRCP Commands sent from the remote rendering device.
When the AVRCP Target profile is selected, the Playback Status Event checkbox
on the Bluetooth Settings panel allows you to enable or disable Playback
Status. This setting is enabled by default. Toggling this setting will
disconnect any active connection.
When the AVRCP Target profile is selected, and Playback
Status Event is enabled, you can navigate to Actions > A2DP Sink/AVRCP >
Playback Status to open a dialog to set a response to the remote AVRCP
Controller (sink) device. The Playback Status control provides a menu that has
the following options: Auto, Stopped, Playing, Paused, Fwd Seek, Rev Seek,
Error. The default selection is Auto.
For any choice except Auto, the selected Playback Status will be passed to the
AVRCP Controller device.
If Auto is selected, APx will set the status to Playing when the generator is
turned on. When A2DP streaming is started, the playback status will be Paused
when the generator is off. When A2DP streaming is stopped, the playback status
will be Stopped when the generator is off.
The Playback status value is only updated when the active audio stream is
A2DP. Playback status changes should not be made when the audio path is SCO.
Absolute Volume
AVRCP Absolute Volume control features are not supported by the Legacy
Bluetooth Option.
AVRCP Absolute Volume Control is a feature introduced in AVRCP 1.3. This
feature is intended to allow the source device to specify a percentage value
of full volume to the rendering device (speaker or headphones).
The rendering device responds with a notification of the current absolute
volume level.
APx supports features of Absolute Volume Control in both the AVCRP Controller
(A2DP sink) and Target
(A2DP source) profiles.
AVCRP Controller profile
In the AVRCP Controller profile, APx acts as a A2DP rendering device (a sink
such as a speaker or headphone), receiving an audio stream from a remote media
player.
APx uses AVRCP Commands to control the remote media player.
When the AVRCP Controller profile is selected, the Absolute Volume checkbox on
the Bluetooth Settings panel allows you to enable or disable Absolute Volume.
This setting is enabled by default. Toggling this setting will disconnect any
active connection.
When Absolute Volume is enabled in the AVRCP Con-troller profile and the
remote Target (source) device supports Absolute Volume, you can navigate to
Actions > A2DP Sink/AVRCP > Absolute Volume to open a dialog to set an
Absolute Volume level value, which can be read by the remote AVRCP Target
device. Values are integers from 0-127. If the Target device does not support
Absolute Volume, this control is unavailable.
…in a sequence
When the AVRCP Controller profile is selected, a sequence step is available to
set the Absolute Volume level on the A2DP sink device. When the step is
included in a sequence and loaded on an APx analyzer that does not support
Absolute Volume, an error occurs when the step is executed. When the step is
included in a sequence and loaded on an analyzer that supports Absolute
Volume, but connected to a remote device that does not support it, an error
occurs when the step is executed.
In a sequence when the AVRCP Controller profile is selected, and the remote
AVRCP Target device sup-ports Absolute Volume, the Absolute Volume level set
in the local A2DP sink device (the APx analyzer) is displayed on the report
for each measurement in the sequence.
AVRCP Target profile
In the AVRCP Target profile, APx acts as an A2DP source device, sending an
audio stream to a remote rendering device (speaker or headphones). APx
responds to AVRCP Commands sent from the remote rendering device.
When the AVRCP Target profile is selected, the Absolute Volume checkbox on the
Bluetooth Settings panel allows you to enable or disable Absolute Volume. This
setting is enabled by default. Toggling this setting will disconnect any
active connection.
When Absolute Volume is enabled in the AVRCP Target profile and the remote
AVRCP Controller (sink) device supports Absolute Volume, you can navigate to
Actions > A2DP Sink/AVRCP > Absolute Volume to open a dialog to send an
Absolute Volume command to the remote AVRCP Controller device. Values are
integers from 0-127. If the remote AVRCP Controller device does not support
Absolute Volume, this control is unavailable.
When the AVRCP Target profile is selected, and the remote AVRCP Controller
device reports its Absolute Volume level, the level is read and displayed in
the APx Bluetooth Monitor. If the remote device does not support Absolute
Volume control, the Bluetooth Monitor indicates “N/A” for this value.
When the AVRCP Target profile is selected, a nested sweep parameter called
“Absolute Volume” is available. This parameter allows the AVRCP Controller
(A2DP sink) device manufacturer to test audio output at various levels,
plotted on one graph.
…in a sequence
When the AVRCP Target profile is selected, a sequence step is available to
set the Absolute Volume level on the remote device. When the step is included
in a sequence, and loaded on an APx analyzer which does not support Absolute
Volume, an error occurs when the step is executed. When the step is included
in a sequence, and loaded on an analyzer that does support Absolute Volume,
but the remote device does not support it, an error occurs when the step is
executed.
In a sequence when the AVRCP Target profile is selected and the remote AVRCP
Controller device supports Absolute Volume, the Absolute Volume level reported
by the remote device is read by APx and displayed on the report for each
measurement in the sequence.
Commands Change Generator Settings
When APx is configured for A2DP Source AVRCP Target, the APx generator can
now respond to certain AVRCP commands.
AVCRP Target profile
In the AVRCP Target profile, APx acts as an A2DP source device, sending an
audio stream to a remote rendering device (speaker or headphones). APx
responds to AVRCP Commands sent from the remote rendering device.
When the AVRCP Target profile is selected, the Commands Change Generator
Settings checkbox on the Bluetooth Settings panel allows you to enable or
disable this feature. This setting is enabled by default.
AVRCP generator commands are only acted upon when the active measurement has a
generator with an ON/OFF button, and the generator is not disabled.
Commands
- The AVRCP command Play turns the generator On
- The AVRCP command Pause turns the Generator Off
- The AVRCP command Stop turns the Generator Off, and stops A2DP streaming.
- The AVRCP command Next Track increases the generator Frequency equivalent to press ing the up arrow on the frequency control in the panel
- The AVRCP command Prev Track decreases the generator Frequency equivalent to pressing the down arrow on the frequency control in the panel.
- The AVRCP command Volume Up increases the generator Level on Ch1 equivalent to pressing the up arrow on the level control in the panel. Volume Up messages are not received in legacy Bluetooth modules.
- The AVRCP command Volume Down decreases the generator Level on Ch1 equivalent to pressing the down arrow on the level control in the panel. Volume Down messages are not received in legacy Bluetooth modules.
Steps in connecting APx to a Bluetooth device
There are 3 steps involved in setting up a connection between any Bluetooth
devices. APx500 software provides more visibility and control of options for
these communication steps than most DUTs.
-
Discovery
Discovery scans the area and lists any Bluetooth devices that are not “undiscoverable” (hidden).
Many devices are undiscoverable by default, and must be set to a discoverable mode through a switching sequence. -
Pairing
Pairing establishes a mutual, secure relationship between devices that have at least one compatible profile.
Pairing is stored in non-volatile memory in each device. Devices can pair with more than one other device. -
Connection
Paired devices can connect using compatible profiles and roles. Connection enables exchange of audio or control data. Each device can connect with only one device at a time.
Process for discovery, pairing and connection
Actions Dialogs
Bluetooth Actions are commands that can be sent from the APx analyzer to the
Bluetooth device. The current Bluetooth profile(s) and connection determine
which commands are available in the Bluetooth Actions dialog box. Bluetooth
Actions for A2DP Source, HFP AG, AVRCP Target
For this profile set, these actions are available:
A2DP Source
For A2DP Source, the actions are
-
Start Streaming / Stop Streaming
HFP Audio Gateway
For HFP Audio Gateway, the actions are -
Open SCO
-
Dial
-
Ring
-
Close SCO
-
Hangup
A “SCO” is a “Synchronous connection-ori-ented” link, which is the type of
radio link Bluetooth uses for voice data. The SCO link is used in the APx
supported protocols HFP and HSP.
Bluetooth Actions for A2DP Source, HSP AG, AVRCP Target
For this profile set, these actions are available:
A2DP Source
For A2DP Source, the actions are
-
Start Streaming / Stop Streaming
HSP Audio Gateway
For HSP Audio Gateway, the actions are -
Open SCO
-
Close SCO
-
Ring
Bluetooth Actions for A2DP Sink, HFP Hands Free, AVRCP Controller
For this profile set, these actions are available:
A2DP Sink/AVRCP
For A2DP Sink/AVRCP, click the
- AVRCP…
button to open the Send AVRCP Command transport controls panel:
HFP Hands-Free
For HFP Hands Free, the actions are
-
Answer
-
Reject Call
-
Hangup
-
Open SCO
-
Close SCO
AT Commands
For AT Commands, click the -
AT Commands…
button to open the Send AT Commands panel. See page 140.
Bluetooth Actions for
A2DP Sink, HSP Headset, AVRCP Controller For this profile set, these actions
are available:
A2DP Sink
For A2DP Sink/AVRCP, click the
- AVRCP…
button to open the Send AVRCP Command transport controls panel:
HSP Headset
For HSP Headset, the actions are
- Button
- Open SCO
- Close SCO
Bluetooth: Send AT Commands Dialog You can open the Send AT Commands
dialog by clicking Actions > AT Commands from Signal Path Setup, or from the
context menu opened by right-clicking in the Bluetooth Monitor.
You must have an APx input or output configured for Bluetooth, and be paired
and connected to an appropriate Bluetooth HFP profile device.
Phone Call
To make a phone call, enter a new phone number in the Number field and click
Call, or click Redial Last Number. Disconnect a phone call by clicking
Hangup.
AT Command
Enter any valid AT command as a text string, and click Send to transmit the
command to the connected device.
More About Bluetooth…
General
Bluetooth is a short-distance (a few meters) control, data, and audio
communications wireless technology. Bluetooth replaces wires in the user’s
“personal area.”
Bluetooth uses low power, frequency-hopping radio in the 2.4 GHz band.
Communication is two-way (for handshaking, metadata, etc); some profiles (HFP,
for example) support duplex audio (both directions simultaneously); some
profiles (A2DP) support only simplex audio (one direction per connection).
Typical uses are mouse, keyboard, cell phone, headphones, hands-free talk and
listen.
APx Bluetooth Option
An APx Bluetooth Option module must be fitted in the analyzer instrument to
enable Bluetooth transmission and reception. See Bluetooth Option on page 9.
Bluetooth Profiles
Bluetooth has about 30 “profiles” that describe the capabilities and/or
current operating modes for Bluetooth devices.
For devices to communicate, they must support and share a common profile.
For example, a wireless mouse uses the “HID” profile, which has no audio
capabilities. Wireless headphones use the “A2DP” profile, which has no cursor
control capabilities. The Bluetooth profiles these devices use are not
compatible with each other.
APx supported profiles
The APx Bluetooth Option supports four Bluetooth profiles.
The supported profiles are
-
A2DP (Advanced Audio Distribution Profile)
This is a one-way (source or sink), relatively highquality stereo audio profile. -
HFP (Hands Free Profile)
This is a bi-directional voice communications audio profile that includes AT- type commands for phone use. Legacy Bluetooth DUTs support only the CSVD codec at sample rate of 8 kHz; HFP 1.6 compatible DUTs support the wideband voice mSBC codec at a sample rate of 16 kHz. -
HSP (Head Set Profile)
This is a simpler version of HFP, using the CSVD codec at 8 kHz and a reduced set of AT commands. -
AVRCP (Audio Video Remote Control Profile)
This provides Play-Pause-Forward-Reverse “remote control” transport-type commands to control an audio source. This profile is typically used in conjunction with A2DP for personal audio player applications.
More about Supported Bluetooth Profiles
HSP
HSP is the “Head Set Profile.” This profile supports voice-quality audio,
using the CVSD codec at 8 kHz sample rate. This profile is used for phone-to-
headset communication.
Roles
Supported roles are AG “Audio Gateway” (the phone) and HS “Headset”.
Audio
Audio flows in a duplex (bi-directional) mode, connecting the Audio Gateway
device to the Headset device.
Actions
A subset of AT commands are also supported for phone operations.
HFP
HFP is the “Hands Free Profile.” This profile supports voice-quality audio,
using the CVSD codec at 8 kHz sample rate or the HFP 1.6 “wideband speech”
mSBC codec at 16 kHz. This profile is used for phone-toheadset communication
and for phone-to-car kit hands free communication.
Note: HFP 1.6 wideband speech is only available if the mSBC codec is supported by your Bluetooth module hardware. See Bluetooth Option on page 9 for more information.
Roles
Supported roles are AG “Audio Gateway” (the phone) and HF “Hands Free” (the
headset or car kit mic/ speaker).
Audio
Audio flows in a duplex (bi-directional) mode, connect- ing the Audio Gateway
device to the Hands Free device.
Actions
A subset of AT commands are also supported for phone operations. Compared to
HSP, HFP provides a few more AT commands for hands-free convenience, such as
last number redial.
A2DP
A2DP is the “Advanced Audio Distribution Profile.” This profile supports
higher bit rate, higher performance stereo audio.
Roles
APx supported profile roles are “source” (transmitting audio) and “sink”
(receiving audio). Audio is distributed in one direction only, from the source
device to the sink device.
Audio
The SBC codec is mandatory; Audio Precision Blue- tooth Options also support
the aptX codec. The Bluetooth Duo option also supports aptX HD, aptX Low
Latency and AAC codecs. In A2DP Source, the APx Bluetooth transmitter mutes
the audio when the average signal level falls below –54 dBFS for more than 1
second. We recommend maintaining test levels above –54 dBFS for meaningful
results.
AVRCP
AVRCP is the “Audio/Video Remote Control Profile.”
This profile is used in conjunction with A2DP, and provides “transport”
controls such as Play, Pause, Reverse, Forward, etc.
Roles
Supported profile roles are “controller” and “target.” Note: when APx is the
target, AVRCP commands are ignored.
More about Bluetooth SSP (Secure Simple Pairing) Mode
SSP is required for devices using Bluetooth v 2.1 and later. Bluetooth v 2.0
and earlier devices use Legacy Pairing.
APx provides four SSP (Secure Simple Pairing) options. You must choose the
option that is appropriate for the Bluetooth device you are testing.
Man-in-the-middle (MITM)
Man-in-the-middle or MITM is the term used in Bluetooth technology to refer to
Secure Simple Pairing mechanisms that require human interaction. One device
may display a PIN, for example, and the user may be required to enter the same
PIN using a keyboard on a second device. MITM methods add security to the
pairing process.
APx SSP Modes
Just Works
This mode is used in Bluetooth device relationships that require little
security, such as headsets. User interaction is not required.
Numeric Comparison, Display Only
Some Bluetooth devices have only a display screen to interact with a user; an
example is a car kit (car stereo head unit). Use this mode when APx is playing
the role of such a device.
A use case would be testing a smart phone. APx would be an A2DP Sink, HFP with
a display only (the car kit), and the DUT would be the smart phone. The phone
would initiate pairing, and APx would display the PIN transmitted from the
phone. The user would confirm (using a button on the phone) that the PIN
displayed in APx matched the PIN on the phone.
Numeric Comparison, Display+Buttons
Some Bluetooth devices have a display screen and one or more buttons to
interact with a user; the button may be used for a binary (Yes/No) response to
a query. An example is a smart phone. Use this mode when APx is playing the
role of such a device.
A use case would be testing a car kit. APx would be an A2DP Source, HFP Hands-
Free with a display and buttons (the smart phone), and the DUT would be the
car kit. APx would initiate pairing and transmit a PIN to the DUT. The DUT
would display the PIN, and the user would confirm (using a button in the APx
prompt dialog) that the PIN in the DUT display and the APx PIN matched.
Numeric Comparison, Keyboard
Some Bluetooth devices have a numeric or alphanu-meric keyboard to interact
with the user. An example is a computer used as an audio source, distributing
iTunes audio to a home entertainment system. Use this mode when APx is playing
the role of such a device.
There are not obvious use cases in audio test for this mode, which is include
in APx for completeness. A non-audio test use case would be pairing a
Bluetooth keyboard to a tablet computer. The computer would display a PIN, and
the user would enter a PIN (using the keyboard) that matches the PIN on the
tablet screen.
Legacy Pairing
Bluetooth v2.1 and later devices (such as APx) are per-mitted to use Legacy
Pairing modes when pairing with a Bluetooth v2.0 or earlier device.
Glossary of Bluetooth terms
These terms are used in the Audio Precision Bluetooth audio testing
implementation.
A2DP
is the Advanced Audio Distribution Profile, with two roles: source and sink.
This profile supports higher bit rate, higher performance stereo audio, with
sample rates up to 48 kHz.
The SBC codec is mandatory; codecs such as mp3, AAC, apt-X and others are
optionally supported.
AG
is the duplex Audio Gateway role, used in HFP and HSP. AG is the node (such as
a car kit) that mediates between the user and the mobile phone.
apt-X
is an optional high-performance codec used in A2DP.
AT command
is an audible signal used to control a device. AT commands are a PSTN (Public
Switched Telephone Network) legacy.
AVRCP
is the “Audio/Video Remote Control Profile.” This profile is used in
conjunction with A2DP, and pro-vides “transport” controls such as Play, Pause,
Reverse, Forward, etc. Roles are Controller and Target.
Connect
Paired devices can connect using compatible profiles and roles.
Connection enables exchange of audio or control data. Each device can connect
with only one device at a time.
CVSD
is Continuously Variable Slope Delta modulation, the codec used in HSP and
legacy HFP profiles.
With HFP 1.6, higher data rates enable the use of a higher quality codec
called mSBC.
Device address
Every Bluetooth device has a unique 48-bit device address, in APx500
displayed in hex format, such as 00:f4:b9:c3:a0:cc.
Device class
A Bluetooth device class is a code that identifies the type of device. Some
Bluetooth devices will only recognize devices of a certain class.
Discovery
Bluetooth devices that are not paired can discover each other when they are
in range. Some devices allow users to make the device undiscoverable.
duplex
refers to a bi-directional audio channel, across which speaking and
listening can occur simultaneously.
eSCO
Extended SCO, available in the Bluetooth 1.2 specification. Adds new packet
types (EV1, etc.) and more flexibility in channel parameters, allows
retransmission of bad packets. Also see SCO.
EV1
First of a series of packet types available with eSCO, as opposed to the
HV1, etc. packet types in SCO.
Friendly name
is an optional name for a Bluetooth device, more easily understood and
remembered than the device address. An example is “iPhone”.
HF
is Hands Free, the duplex “phone” role in the HFP profile.
HFP
is the Hands Free profile, intended to allow handsfree device operation in
an automobile. It is similar to HSP, with more phone controls. Roles are AG
and HF.
HFP 1.6
is a revision of the HFP specification, which allows new packet types and
higher data rates compared to legacy HFP. These data rates and newly supported
codecs such as mSBC enable WBS (Wideband Speech) performance.
HS
is Head Set, the duplex “phone” role in the HSP profile.
HSP
is the Head Set profile, intended to enable Bluetooth mobile phone use. Roles
are AG and HS.
HV1
First of a series of packet types available with SCO, as opposed to the EV1,
etc. packet types in eSCO.
Link key
is a shared secret exchanged in pairing.
mSBC
is a monaural version of the SBC codec, optimized for use in the HFP 1.6
profile. This codec and the higher available sample rates enable Wideband
Speech operation.
Pair
Bluetooth devices that have discovered each other can be paired by exchanging
a link key to form a bond. For some devices, pairing is automatic upon
discovery; for others, user interaction is required.
Pairing establishes a mutual, secure relationship between devices that have at
least one compatible profile. Pairing is stored in non-volatile memory in each
device. Devices can pair with more than one other device.
PIN code
A Personal Identification Number embedded in a device or provided by a user
that is exchanged in a pairing negotiation.
Profile
One of a number of defined Bluetooth relationships covering a range of devices
and use cases. A device can support more than one profile, and devices can be
paired acknowledging more than one profile.
role
A role is a defined use of a device within a profile. In A2DP, for example,
the roles are source and sink.
For HFP, the roles are AG and HF.
SBC
(Sub-band Codec), the mandatory codec for the A2DP Profile. Other codecs are
allowed.
SCO
is a synchronous connection oriented channel, a full duplex data channel with
64 kbit/s data rate in each direction. The CVSD codec is used, and the three
HV types of data packets are available. Also see eSCO.
sink
is the term used for the device that receives audio in a uni-directional
system.
source
is the term used for the device that transmits audio in a uni-directional
system.
SSP
is Secure Simple Pairing, the pairing methods required in Bluetooth v2.1.
Audio Precision supports the SSP Just Works, Numeric Comparison and Passkey
Entry methods.
Per FCC 15.19(a)(3) and (a)(4) This device complies with part 15 of the FCC
Rules. Operation is subject to the following two conditions: (1) This device
may not cause harmful interference, and (2) this device must accept any
interference received, including interference that may cause undesired
operation.
Per FCC 15.21, CAUTION to the USER- changes or modifications not expressly
approved by AUDIO PRECISION (the party responsible for compliance) could void
the user’s authority to operate the equipment.
8.4 User Manual Notice for Licence-Exempt Radio Apparatus
This device complies with Industry Canada’s licence-exempt RSSs. Operation is
subject to the following two conditions:
- This device may not cause interference; and
- This device must accept any interference, including interference that may cause undesired operation of the device.
NOTICE TO THE USER – This equipment is intended to be used only with the
Antenna Assembly originally supplied. The Antennas are permanently attached to
the front panel. Do NOT substitute or replace the Antennas or the Antenna
Assembly with a different type or design. Contact Audio Precision to order a
replacement Antenna Assembly- The Assembly Part Number is BFT2.TENA.B and
consists of a assembled front panel , permanently attached antennas, and the
LED assembly.
Additional Antenna Information
-
the antennas on the Blue tooth Module are glued to the SMA connectors to prevent the use of alternate antennas – this equipment should be used only with the Antenna supplied from the factory – See Item 2 belowPer RSS-GEN section 6.8: https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf08449.html#s6.
This radio transmitter – ISED Certification Number IC:23068-B516BT3 HVIN# APX516BD2 has been approved by Innovation, Science and Economic Development Canada to operate with the antenna type listed below, with the maximum permissible gain ndicated. Antenna types not included in this list that have a gain greater than the maximum gain indicated for any type listed are strictly prohibited for use with this device. -
Use only the antenna assembly provided with the unit – Contact Audio Precision to order a replacement Antenna Assembly- The Assembly Part Number is BFT2.TENA.B
-
Per RSS-102 section 2.6. – To ensure compliance with the Radio Frequency (RF) exposure guidelines, this device must be used at least 20 cm away from your body or nearby persons. Failure to observe this warning could result in the RF exposure levels exceeding the applicable limits
References
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