AKG ACOUSTICS AUDIOSPHERE BAP 1000 Binaural Audio Processor Owner’s Manual

AUDIOSPHERE
BAP 1000
OWNER’S MANUAL
V.12

Please read this manual carefully before operating the equipment.
AUDIOSPHERE
BAP 1000
The AUDIOSPHERE is the first audio processor that provides a realistic auditory perspective over headphones.
In other words, the old dream of combining the advantages of loudspeakers and headphones has come true.

Preface

The AUDIOSPHERE BAP 1000 is a highly innovative product which for the first time provides a realistic auditory perspective when listening through headphones. The music no longer plays inside your head but scems to come from the room, as if you were listening to a real orchestra.
The AUDIOSPHERE BAP 1000 represents many years of painstaking research by AKG scientists in the field of Individual Virtual Acoustics (LV.A.). We use the term “Individual Virtual Acoustics” to describe the kind of acoustic virtual reality the AUDIOSPHERE creates. This is only possible if the features of the lListener’s ears are taken into account. The future oriented LV.A. technology transcends conventional electroacoustics to incorporate discoveries made in psychological and physiological acoustics,
The AUDIOSPHERE is the first audio processor that “failors’ the sound to the user’s ears for optimum reproduction quality. It offers a choice of nine Presct ear transfer curves which provide optimum approximations to nearly any individual set of car transfer curves.
The AUDIOSPHERE has been prepared for a wide range of professional and audiophile applications. Being software controlled, it can also be expanded and updated.
Section I of this manual contains instructions on how to set up and use the AUDIOSPHERE.
Section I is entitled Individual Vimsal Acoustics and includes the scientific background of the AUDIOSPHERE as well as a more detailed description of the unit itself.

Section I; Instructions for Use

1. Precautions
   1.1 When replacing the fuse, use only the correct type for the AC voltage you are using as stated on the next page and in the Specifications.
   1.2 To prevent the unit from overheating, do not cover the ventilation slots in the top panel and be sure to provide adequate ventilation. When placing the umit on a shelf or mounting it in a 19″ rack, leave at least 1 inch of space between the top panel and the next shelf or the unit above it.
   1.3 Slpill no liquids on the wnit and do not drop any objects through the top panel ventilation slots.
   1.4 Do not place the unit near heat sources such as radiators or air ducts, or in a place exposed to dircet sunlight, excessive dust, ‘moisture, rain, mechanical vibrations, or shock.
   1.5 Do not try to open the case. Refer servicing to qualified personnel only.
   1.6 ‘Warning: Using headphones at high volume levels – particularly, over extended periods of time – may damage your hearing,

2. Ins and Outs
   Note:
   Due to the differences in requirements and cable types used in the hi-fi and professional fields, the AUDIOSPHERE s delivered without connecting cables. XLR connectors for custom cables are available from AKG as items 6000H0671 (malc) and making 6000H0670 (female).
   • A digital coaxial/optical S/PDIF digital input interface is available as an option.Fig.1: Rear panel connectors.
   POWER INPUT:
   IEC standard socket with integrated automatic AC voltage selector and fuse hoider.
   Before replacing a blown fuse, unplug the power cord from the POWER socket, (With the power cord inserted, the fuse holder cannot be opened.) Open the fuse bolder directly below the AC connector. Remove the fuse. Insert a new fuse: 1 A slow-blow for 110 VAC; 0.8 A slow-blow for 220 VAC.
   Close the fuse holder.
   ANALOG OUTL,R: Left and right unbalanced line level outputs.
   ANALOGINL, R: Left and right unbalanced line level inputs.
   The input and output XLR connectors are wired in accordance with AES 14-1992 (ANSI §4.48-1992):
   Pin 1: ground
   Pin 2: audio (“hot”)
   Pin 3: ground
   To comnect the AUDIOSPHERE to RCA inputs and outputs, use a single-conductor shiclded cable with an XLR connector at one end and an RCA plug at the other end for each channel. Be sure to bridge pins 1 and 3 in the XLR connector. PHONES:
   4-pin male XLR connector accepting the AKG K 1000 headphones. The connector is wired as follows:
   Pin 1: Left channel, audio
   Pin 2: Left channel, ground
   Pin3: Right channel, audio
   Pin 4 Right channel, ground
   To connect headphones with a %” TRS (stereo) jack plug, use the supplicd XLR to TRS adapter.

3. Connection to Playback Systems
   The AUDIOSPHERE provides line level inputs and outputs on 3-pin XLR connectors (ANALOG IN L/R, ANALOG OUT L/R) and 2 headphone output (PHONES) on a 4- pin XLR connector. The PHONES output is driven by a conventional amplifier which is capable of driving any type of headphones including the AKG K 1000 In order to achicve true high-end audio quality, particularly if you use an AKG K 1000, you may connect an external amplifier to the ANALOG OUT sockets on the rear panel of the AUDIOSPHERE (see fig6).
   Figs. 3 through 6 show some typical examples of how to connect the AUDIOSPHERE to a playback system. The same basic rules apply to virtually any system configuration.Fig.3 shows a basic configuration comprising only a CD player, the AUDIOSPHERE, and a pair of headphones. Connect the ANALOG IN sockets on the AUDIOSPHERE rear panel to the LINE OUT sockets on the CD player. Use a stereo cable (or two mono cables) with male XLR connectors at one end and male RCA plugs at the other end.
   Connect the headphones to the PHONES output on the AUDIOSPHERE front panel see fig.2.
   If you use an analog turntable and preamoplifier, cassette or DAT deck, or other playback equipment, be sure to connect the AUDIOSPHERE to the LINE OUT sockets on the playback device or preamp.Fig.4 shows how to connect the 4UDIOSPHERE to a system built around an integrated amplifier. Connect the AUDIOSPHERE to a pair of LINE outputs on the amplifier, using RCA to 3-pin XLR cables. Connect the headphones to the PHONES output on the AUDIOSPHERE front panel (see fig. 2).Fig.5 shows how to connect your K 1000 headphones to an unused pair of loudspeaker terminals on your amplifier.
   Connect the left and right TAPE OUT sockets on your amplifier to the left and right ANALOG IN sockets on the AUDIOSPHERE. Then connect the left and right ANALOG OUT sockets on the AUDIOSPHERE to the left and right TAPE IN sockets on the amplifier. Use 3-pin XLR to RCA cables.
   Connect the stripped and tinned leads of the K 1000 adapter cable to the unused loudspeaker terminals. The leads are color coded as follows:
   ‘White: Left channel audio
   Black: Left channel ground
   Red: Right channel audio
   Blue: Right channel ground
   Note:
   ‘When listening over loudspeakers, be sure to switch the AUDIOSPHERE power OFF.
   This will cause the bypass relays in the AUDIOSPHERE to route the input signal straight through to the output.Fig6 shows how to conncct the AUDIOSPHERE to a video system. Connect the AUDIOSPHERE to the audio line outputs of the video equipment. Comncct the headphones to the PHONES output.
   Alternatively, you may use a dedicated headphone amplifier, e.g. the AKG A 1000 for the K 1000 beadphones. Connect the amplifier as shown, referring to the amplifier manual for connector types, pinouts, and cable wiring.
   Note:
   ‘When playing back dummy head recordings, make sure to press the BYPASS key on the AUDIOSPHERE to prevent the binaural processing from defeating the special dummy head effect, Otherwise the dummy head recording would sound as if it were played back through a pair of loudspeakers!
   • The signals delivered by the AUDIOSFHERE are not_suited for loudspeaker u but should only be played back over headphones!
   Therefore, if you insert the AUDIOSPHERE between an audio source and an amplifier which you also use to drive loudspeakers (see fig.5), be sure to always switch the AUDIOSPHERE power OFF when listening over loudspeakers. This will cause the bypass relays in the AUDIOSPHERE to route the input signal straight through to the output.

4. Controls POWER:
   Switches the power to the AUDIOSPHERE ON or OFF.
   On switching ON, the AUDIOSPHERE will run a sclf-test indicated by the letters “BAP” in the PROGRAM window.
   As soon as the self-test is completed, the system will load Internal Preset no. 1. I you have inserted a ROM Card into the CARD slot, the AUDIOSPHERE will automatically load the first Preset on the ROM Card.
   SENSITIVITY:
   Adjusts the inlgut gain of the AUDIOSPHERE. Adjust the that the red clipping LEDs next to the control input gain so knob will not light during playback.
   PHONES:
   4-pin XLR socket for connecting the AKG K 1000. To connect headphones with a %” TRS jack plug, use the supplied XLR to TRS adapter.
   VOLUME:
   Adjusts the volume level of the PHONES output.
   PROGRAM:
   In the normal Listening mode, the PROGRAM window indicates the active Preset number. In the Test mode, the number will blink, It may also be used to display information about the ROM Card being used, ete.
   CARD key:

Toggles between the Internal ear transfer curve Presets and the External Presets on the ROM Card. When you press the  CARD key to activate the ROM Card the yellow LED to  the left of the key will light. The last active Preset number in  the storage medium you are leaving remains in memory.

When you press the CARD key again you will return to the  original Preset. This allows you to toggle between Internal  and ROM Card Presets with different numbers.
(–CARD key)
‘When a ROM Card is in the CARD slot you can make its software release number (e.g, ‘vl1″) appear in the PROGRAM window by pressing the CARD key twice briefly in rapid succession (like you would “double click” an icon with a computer mouse).
BYPASS:
Pressing the BYPASS key causes the input signal to be routed straight through to the ANALOG OUT and PHONES outputs. This modc defeats the binaural processor s0 you will listen through your headphones in the conventional way.
The AUDIOSPHERE automatically adjusts the output level to optimally match the loudness of the processed Sens te allow A/B comparisons with conventional one reproduction.
When the ROM Card is active (yellow CARD LED lights) the AUDIOSPHERE will use a level setting stored on the ROM Card. In this mode the signal passes through the processor as well as the A/D and D/A converters.
There is also a “hardwire” bypass. When you switch the power OFF, the inputs will be physically connected by relays to the outputs. Ifyou have inserted the AUDIOSPHERE between an audio source and an amplifier (see fig5) you should use this function before switching to loudspeaker reproduction.
To bring up the release number of the software installed in the AUDIOSPHERE, double click the BYPASS key. The number will appear in the PROGRAM window, oe. vi3- 2.1″. The first two digits show the highest ROM Card software version (in this example, “1.3″) which is compatible to the Internal software version (tbe last two digits, in this example, 2.1″).
MUTE:
Mutes the PHONES and ANALOG OUT outputs.
The MUTE key also allows you to leave the Test mode by a “double click”, The PROGRAM window display stops blinking and changes to “XR”.
1…9:
These keys select one of nine Internal or External car transfer curve Presets. Refer to the Test CD Booklet for instructions ow how to select your optimum personal Preset.
Key 1 also allows you to enter the Test mode by a “double click”. The letter “R” appears in the PROGRAM window and the display starts blinking. When you sclect a Preset, the letter “R* will flash briefly in the PROGRAM window before the Preset number is displayed.
CARD sult:
Accepts AUDIOSPHERE ROM Cards. Insert the ROM Card with the contact side up. To activate the card, press the CARD key. It is not necessary to switch the power OFF before inserting or removing a ROM Card.

5. Selecting Presets
   Spatial hearing depends on the listener’s ear transfer curves which differ widely from person to person (see Section IL, chapter 12.). To ensure optimum reproduction, these differences have to be taken into account. Therefore, the AUDIOSPHERE can be individually adjusted to the user. Having connected the AUDIOSPHERE to your audio or video system, make enough time for finding your personal, optimum ear transfer curve Preset.
   n a number of specially devised test serics, nine statistically representative sets of ear transfer curves were selected from a host of measurements and integrated as Presets into the AUDIOSPHERE. Our experience shows that 90% to 95% of all listeners will find a Preset that provides an optimum approximation to their individual set of ear transfer curves. The differences in sound between the Presets make it immediately obvious why this matching of ear transfer curves is imperative.
   As an alternative to the Internal Presets, you may have your own ear transfer curves measured. The resulting data will be stored on a ROM Card. For details on individual ear measurements, contact your local AKG representative.
   Finding the “best fitting” Preset requires some expericace in critical listening. To facilitate the task, a Test CD with suitable test signals produced by AKG is supplied with the AUDIOSPHERE, Insert the Test CD into your CD player and follow the instructions in the Test CD booklet. The Test Sheet contained in the Appendix to this Manual helps you evaluate each Preset.

Note:
In addition to the laws of acoustics, hearing as part of the human perception system is subject to many other influences, which have a bearing on the AUDIOSPHERE listening experience:

1. You may at first have difficnity localizing the sound in front of you. This is because your cars receive the appropriate cues but you do not see the sound source in front of you.
   Therefore, we recommend to close your cyes, particularly while selecting the optimum Preset.

2. The AUDIOSPHERE has been designed to reproduce as faithfully as possible the information contained in a recording. This means that you may sometimes notice shortcomings in the stereo perspective of a recording which might remain hidden when played back through loudspeakers or be ignored in casual listening.

3. The AUDIOSPHERE provides a highly realistic listening experience by preventing sound localization inside the head, the main disadvantage of conventional headphones.
   Therefore, do not expect any fancy “effect” (such as room simulation or surround sound) from the AUDIOSPHERE.

4. Sound localization in the open can be elusive. Just think of how difficult it is to localize the chirp of a cricket. So, do not expect more from binaural simulation than what is possible in real life!

5. Conventional headphones expand the stereo spread from the 60° typical of loudspeaker reproduction to 180°. The AUDIOSPHERE compensates for this distortion but you may at first perceive this as a narrowing of the stereo spread.

6. In order to appreciate fully all the advantages of the AUDIOSPHERE, it is necessary for our perception system to discard some old habits and expectations. This may take some time and effort. But after a few days or weeks you will have grown accustomed to the new listening experience and hardly believe you ever enjoyed listening over conventional headphones.

Section II: Individual Virtual Acoustics

The AUDIOSPHERE is a totally new approach to sound reproduction. AKG decided to call the philosophy behind the AUDIOSPHERE “Individual Virtual Acoustics’ (LV.A.). The term suggests that the technique is related to Virtual Reality in that it reproduces sound in the most realistic manner possible.
The breakthrough for the AUDIOSPHERE came when the researchers at AKG realized that it would e necessary to create @ process which models the way the user’s ears “shape” the impinging sound. This involved looking beyond the fimits of physical acoustics within which audio manufacturers normaly operate. Physiological and psychological acoustics as parts of a general theory of perception provided new insights into the mechanisms of binaural, or “spatial’, hearing.

1. The Problem
   1.1 Inherent Drawbacks of Headphones
   Headphones have several advantages over loudspeakers. easier to control and will therefore reproduce audio signals more precisely. They allow you to listen at high volume levels without dismrbiumur neighbors. Fmalldyéatihe sound is not affected by the acoustics of the listening room which may be less than ideal.
   Conventional headphones, however, have one major drawback: they severely distort the auditory perspective, They squeeze all the sound into the space between the carcups so the orchestra ends up playing inside the listener’s head. This effect called “inside localization” is obviously the direct opposite of realistic reproduction.
   In the past, there have been many unsuccessful attempts to overcome this disadvanm&e.
   Even the most technically sophisticated headphone models are incapable of making the individualdinstrumcnts of an orchestra seem to play in the room rather than inside the user’s head.
   1.2 Inside Localization
   Researchers and designers have probably been struggling with inside localization since the first pair of headphones was built. Some of the theories developed were quite bizarre and ignored discoveries about directional hearing which had been made much earlier.
   Even after 1950 inside localization was thought to be caused, ¢.g., by resonances of microphones or headphones, overmodulation of the nervous system, or the fact that the sound waves from headphones hit only the cars, not the body. Reichardt and Haustein PI in 1968 speculated for the first time that inside localization might be due to the headphones eliminating all the influences the sound waves are subjected to on their way from the sound source to the listener’s tympani. The diagrams on the following pages illustrate this hypothesis.
   Most recordings are mixed for playback through loudspeakers. Listening to a pair of loudspeakers is similar to looking at a theater stage as the sound is spread between the loudspeakers, with a more or less ‘dramatic sense of depth.Fig. 8 shows a standard stereo listening situation. A pulse-shaped signal, e.fi:dmmbeat, that has been hard left by the recording panned engineer will be projected by the left- hand loudspeaker only as shown. The drum beat arrives at the listener’s head from an angle of 30°. The listener perceives the louds) er as & point source and normally finds it easy to localize it acoustically. If the signal is measured right in front of the two tympani, then the oscilloscope traces of its impnuise responses (amplitude vs. time) show that the sound has been severely “deformed”. On its way from the loudspeaker to the two tympani it has been modified by various physical influences. It is obvious that the sound will arrive at the left ear before arriving at the right ear. Due to the acoustic “shadow” cast by the head, the sound mlure level at the right ear is lower that at the left ear. Other effects include reflections off the shoulders, diffraction, and pinna resonances.
   The outer car (which in this context includes mot only the ear canal and pinna but the head and trunk as well) therefore acts as a filter which modifies every sound signal depending on its angle of incidence and frequency. The linear distortion of the amplitude and phase resulting from the signal filter action of the outer ear can be described by the so-called complex outer ear transfer function (for the sake of simplicity, we will call it the ear transfer curve from now on). All of the effects mentioned above add to every sound characteristic cues from which our brain can “compute” its location. Precisely how the sound is modified depends on the shape of the ears, head, shoulders, actually the whole body, so this process differs from person to person. Fig9 shows the ear transfer curves for five persons with normal hearing. All measurements were made in exactly the same conditions. The graphs clearly show differences of more than 10 dB in important frequency ranges.
   When a stereo signal is played back through headphones, the semse of depth is lost, the stereo spread is narrowed, and the music plays inside the head. What happened?
   In contrast to a natural situation, fig.10 on the pext page shows the situation in conventional headphone listening.The electrical transfer climinates the modification of the sound by the body. The brain will receive none of the cues from which it normally deducts the location of a sound source. Instcad, the auditory tract/brain system interprets the sounds as located between the ears.
   This problem of inside localization has been the “hallmark” of headphones up to now.
   A drum beat panned hard left will be delivered to your left ear only while your right ear receives no signal at all.
   The sound source appears to be located in your left ear (90° to the icft). Also, this situation causes an unpleasant sense of pressure.
   Signals panned hard right create the egact mirror image situation. Any signals panned in between will be Jocalized on z line connecting the two cars.

2. The Solution: AKG Binaural Processing
   In order to eliminate the problem of inside localization, omc should obviously try to add all the cues required for spatial hearing to the for headphone destined playback. In other words, the signal delivered by the heaphones to the tympani would have to look exactly the same as it would when listezg:!gl, say, to an orchestra in a concert.
   This kind of headphone signals would enable the brain to localize sounds where they originally came from: the rmusic will play in the room rather than inside your head.
   Thus, the signal would have to be modified in the same way as it would be modified in natural hearing. To this end, the left and right stereo signals are cach passed through a pair of electronic ~ circuits {filters) which modify the drum beat of our example exactly as it would be modified on its way from the loudspeakers to the left and right tympani (see fig.11).
   The filters simulate the ear transfer curves for %30° in terms of amplitude and phase.
   The two output signals of the filters assigned to the left and right ears are summed and fed to the left and right earphones. Mcasurements taken at the tympani yield the same results as in a “natural” hearing situation and the brain receives the familiar cues from which it can identify the sound source location. It was not until 1972 that Laws {3] used the setup shown in fig.11 to supply experimental proof for this theory.
   The correct simulation of a pair of loudspeakers by this setup provides for correct imaging of all the sound sources contained in the recording, with all their features including localization cues.
   Techniques used to achieve this are called “binaural audio” because we use two ears to hear (scientists might say that *human hearing is binaural’). In much the same way as three-dimensional vision depends on two cars, three- dimensional, or spatial, hearing relies on two ears.
   Making this fairly obvious solution work, though, is very complex and costly and has become feasible only recently through the use of high technology. Measurements in the ear canal, for instance, require special miniature microphones and test routines, and the simulation of ear transfer curves by digital filters was not possible before high-power microprocessors and fast signal processors became available.
   Note:
   Binaural processing does not “distort” the signal in order to achitve some artificial effect.
   This would defeat the purist approach of restoring the same auditory cues that you would receive when listening through 2 pair of loudspeakers, leaving the balance and timbre of the recording intact.

3. Creating the AUDIOSPHERE
   3.1 AKG and Binanral Processing
   AKG has been studying the problem of three-dimensional reproduction of sound signals over headphones for many years and has mad:‘fi’cat efforts in this area, particularly over the last few years. Thanks to this internationally recognized, pioneering work, AKG is now leading the way in this field. As carly as 1987, AKG developed the CAP 340M, a digital signal processing system whose computing power of 340 MFLOPS put it in a line with the fastest super computers of the time [4, 5, 6]. The system for the first time made investigations in the field of binaural audio both simple and efficient. Also in 1987, researchers at AKG wrote a simulation program which enables the user, wearing headphones, to move around acoustically in a simulated room. This was in fact an early application of Virual Acoustics 5, 6]. AKG developed dedicated measurement and simulation techniques in order to investigate the fundamental parameters of spatial hearing with the aid of digital signal processing [7, 8].
   In October 1991, a binaural processor designed by AKG, basically a single- channel version of the AUDIOSPHERE, was successfully used in the AUDIMIR scientific experiment on board the Russian space station MIR to demonstrate for the first time the significance of spatial bearing for human orientation at microgravity [9].
   All these efforts finally led up to the development of the AUDIOSPHERE BAP

4. This Processor has been designed to prevent inside localization in headphone listening and provide at least the same sound quality as high-quality loudspeakers, without compromising on imaging (10, 11).
   32. The AUDIOSPHERE BAP 1000
   The AUDIOSPHERE simulates a defined loudspeaker listening situation through headphones. As shown in fig.11, the AUDIOSPHERE uses a pair of filters for each of the two londspeakers to recreate the direct sound. These filters simulate a pair of stereo loudspeakers placed in the usval way, ie., 30° left and right in front of the listener.
   Several other filter pairs simulate room reflections to model the acoustics of a good listening room.
   Every music production contains a specific ambience as it existed at the recording locale or was added by the sound engineer. Good listening room acoustics will not interfere with this specific ambience. The AUDIOSPHERE has been designed to reproduce the “acoustics’ contained in a recording withont changing it or creating some artiificial ambience. This is much easier to do in a digital simulation than in a real control room or fiving room where ideal acoustic treatment is both difficult and costly to apply. In short, the AUDIOSPHERE is no room simulator in the sense that it would recreate the acoustics of a specific concert hall and superimpose it on the original recording.
   The Internal Presets stored in the AUDIOSPHERE have been derived from ear transfer curves measured on nine subjects in an ideal listening situation, Alternatively, you could bave your own ear transfer curves measured in a real Tistening room in order to simulate exactly this situation. The parameters obtained from the measurement will be stored on an AUDIOSPHERE ROM Card. This service is of particular interest for professional recording and mixing engineers as it allows them to reproduce the same familiar studio acoustics wherever they work.

5. Applications
   The AUDIOSPHERE BAP 1000 binaural processor combines the advantages of headphones and loudspeakers while eliminating their respective shoricomings. This makes headphones suitable for totally new applications. The AUDIOSPHERE will dramatically improve the sound quality of any headphones.
   The AUDIOSPHERE is entirely software controlled. This allows the device to be adapted to different applications and improvements or new functions to be installed later as software updates on ROM Cards.
   The ear transfer curves stored as Presets in the AUDIOSPHERE have been derived from a standard hi-fi listening situation. The AKG K 1000 headphones ensure optimum x:zagmg because they have been designed on the basis of important aspects of spatial earing.
   4.1. Hi-fi
   High quality sound reproduction (in both hi-fi and professional environments) depends on appropriate loudspeakers and a listening room with suitable acoustics. In most cases, it is impossible to create optimum conditions, because it is cither too expensive or too difficult to rebuild the living room. Also, the neighbors may get angry if you turn the volume up too high. The AUDIOSPHERE provides a way for hi-fi enthusiasts to solve all these probiems at an affordable price.
   4.2 Professional Applications
   In the recording studio, the technical and acoustic quality of the monitoring system is of fundamental importance for the mixing and assessment of productions. In addition to the audio equipment (amplifiers, loudspeakers), it is the acoustic properties of the control room that determine the monitor sound quality.
   No matter how carefully the control room has been designed, some problems simply cannot be solved: There is only one sweet spot, or at best a line in the between the mi loudspeakers. So if more than one person is listening, everyone will hear a differcnt balance. So will the sound engineer if they have to move from channel 1 to channel 128 on a large console to adjust an EQ setting on the piano and ‘bring up the tambourine.
   Mobile studios and O/B vans, opera house and theater control booths, and live concerts impose far worse acoustic conditions than recording studios.
   The AUDIOSPHERE allows the studio engineer to use headphones as an altemative to high-quality monitor loudspeakers 10 assess productions, even their stereo perspective.
   Monitoring thus becomes independent of variations or deficiencies in control room acoustics.
   The key to this solution is to simulate an existing, optimum listening situation, For this purpose, the sound engineer’s ear transfer curves will be measured in his or her favorite monitoring position. The data obtained is stored on a ROM Card. A proper headphone simulation should be indiscernible from the sound of the monitor sj rs in the control room, Numerous tests have shown that this is what the AUDIOSPHERE actually does. The AUDIOSPHERE ROM Card scheme thus enables sound engineers to have their familiar control room acoustics ready anytime, anywhere, in the form of a Erecisely reproducible, virtual control room. A mix can be assessed in an O/B van, opera house or theater sound booth, or live mixing position in the same way as in the familiar studio control room. If the user had their ear transfer curves measured in several different rooms, they can check at the push of a button how the same mix would sound in different rooms.

For semiprofessional users the AUDIOSPHERE provides a cost efficient alternative to building their own high quality control room which would be unaffordable for most amateurs, In the future it will be possible to combine the data for a specific monitoring situation with the ear transfer curves measured at the user’s ears. This allows the user to acoustically enter any real or imaginary control room whithout ever having been there in person.
Overdubbing in the studio presents another previously unsolved problem. Inside localization distorts the auditory perspective and thus adds to the stress the unnatural situation in the recording studio already exerts on the musician. Artists whose music depends strongly on their communication with the other musicians (espcially, jazz) are particularly unhappy about this problem. Vocalists often tend to sing flat when overdubbing.
By climinating inside localization, the AUDIOSPHERE provides a much more patural cue signal. This creates a more relaxed atmosphere for the musician and thus improves their performance.

Section III: Appendix

References

1. J. Blavert, “Raumliches Héren’, S.Hirzel Verlag, Stuttgart, Germany (1974); “Raéumiiches Haren, Nachschrift, neue Ergebnisse und Trends seit 1972”, S.Hirzel Verlag, Stuttgart, Germany (1985). (This work gives a detailed introduction to “spatial hearing”.)
2. W. Reichhardt and B.-G. Haustein, “Zur Ursache des Effcktes der “Im-Kopf- Lokalisation”, Hochfrequeuztechnik und Elektroakustik 77 (1968), pp. 183 – 189.
3. P, Laws, “Zum Problem des Entfernungshirens und der Im-Kopf-Lokalisiertheit von Horereignissen’, Ph-D. thesis, Technische Hochschule, Aix-la-Chapelle, Germany (1972).
4. A. Persterer, “CAP Creative Audio Processor – ein Hochleistungssystem zur digitalen Audiosignalverarbeitung’, in Proc. 15th Tonmeistertagung (1988), pp. 405 – 414.
5. A. Persterer, “Ein Hochleistungssystem zur digitalen Audiosignalverarbeitung’, in Fortschritte der Akustik, Proc. DAGA 839.
6. A. Persterer, “A Very High Performan Ore Audio Signal Processing System”, IEEF ASSP Workshop on Applications of Si Processing to Audio and Acoustics, New Paltz, NY (1989).
7. C. Posselt, J. Schrdter, M. Opitz, P. Divenyi, J. Blavert, “Generation of Binaural Signals for Research and Home Entertainment”, in Proc. 12th International Congress on Acoustics, Toronto (1986).
8. FIM Filter Manages”, AKG manual.
9. A. Persterer, M. Berger, Ch. Koppensteiner, Ch. Miiller, M. Nefyodova, M. Opi P, Schnider, “AUDIMIR – Directional Hearing at Microgravity’, meseatod at International Space Year Conference, Munich, Germany (1992).
10. A. Persterer, “Binaurale Simulation des “idealen” Abhorraumes __fiir Kopthirerwiedergabe’, in Proc. 16th Tonmeistertagung (1990).
11. A. Persterer, “Binaural Simulation of an “Ideal Control Room” for Headphone Reproduction’, presented at 90th Audio Engineering Society Convention, Paris, France (1990), preprint 3062.

Specifications

(Measured with Audio Precision System One, output unbalanced; 252 output impedance; GND ON; analyzer bandwidth 22 Hz to 80 kHz; -10 dBV input level))
8/N ratio to DIN 45412:
unweighted:| typically -91 dB flat rms
weighted:| typically -94 dB A-weighted rms
(Values referenced to nominal output level, Input terminated. All values measured with Audio Precision System One, output unbalanced; 258 output impedance; GND ON; analyzer bandwidth 22 Hz to 22 kHz.)
Digital inputs (optional):
coaxial/optical:| to S/PDIF
Max. power requirement:| 80 VA
AC voltage:| 85 VAC to 264 VAC
Fuse:| 110 V: 1 A slow-blow
220 V: 0.8 A slow-blow
Note: Unplug the power cord before replacing the fuse!
‘Temperature range:| 0°C to 45°C to DIN 40046, B1.4
Size (WxHXD):
19″ rack mount version:| 443x88x 324 mm (174×3.5×12.7in.)
483x88x324 mm (19x35x12.7in)
Weight:| approx. 5.4 kg (12 Ibs.)

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