BULLSEYE AUDIO v2.01 Neptune Headphone Calibrator User Manual

BULLSEYE AUDIO v2.01 Neptune Headphone Calibrator

Specifications

• Plugin Formats: VST3, AU, and AAX
• Operating Systems: MacOS and Windows
• Free Trial Period: 14 days

Product Information

NEPTUNE is a corrective audio signal processor designed for Apple EarPods & AirPods (1st & 2nd Gen). It corrects frequency and phase response while incorporating a crossfeed algorithm for a natural soundstage.

• Audio Input (optional pre-processing with Input Gain Slider)
• Crossfeed Algorithm
• Listening Position to Speakers: 6ft
• Filtered Multichannel Delay Line
• Left Channel Dry Signal
• Left Channel Crossfeed Signal
• Left Channel Dry Signal Copy
• 24db/Oct Low Pass Filter at 1600Hz

FAQ

• Q: What are the supported plugin formats for NEPTUNE?
• A: NEPTUNE supports VST3, AU, and AAX formats.
• Q: Is there a free trial period for NEPTUNE?
• A: Yes, all Bullseye Audio Software offers a 14-day fully functional free trial period.
• Q: What are the system requirements for NEPTUNE?
• A: NEPTUNE is compatible with MacOS and Windows operating systems.

Installation

• Open the installer, select your file types, and click continue

• Then click install, and our installer will do the rest

• After installation, run a new plugin scan if your DAW requires it

• Open your plugin and click the button labeled “Demo” or “Enter License”
• Then simply enter your email and or license key to begin using NEPTUNE

System Requirements

• Plugin Formats: VST3, AU and AAX
• Operating Systems: MacOS and Windows

Note: All Bullseye Audio Software has a 14 day fully functional free trial period

Overview

NEPTUNE is a fully comprehensive corrective audio signal processor designed specifically for Apple EarPods & AirPods (1st & 2nd Gen). By leveraging advanced digital signal processing techniques, NEPTUNE corrects both the frequency and phase response of these earphones while incorporating a realistic crossfeed algorithm to emulate the natural soundstage of loudspeaker environments.
NEPTUNE was designed with the specific and deliberate intent to provide users with the highest quality sound reproduction system that is currently possible. To achieve this goal, we must first define the specifics of what a perfect sound reproduction system would entail.

Ideal Sound Quality

• Linear raw unprocessed frequency response
• Linear raw unprocessed group delay response
• Infinitely low distortion
• Crossfeed processing

Below is the selection criteria for identifying sound propagation devices with the highest sound quality potential when paired with the digital signal processing correction techniques that we have available to us.

Selection Criteria

• The sound propagation device must be a headphone
• Eliminates the problems associated with reverberation
• Headphones must be an IEM
• The most direct path from the driver to the eardrum
• Highest possible re-seated measurement consistency
• Raw unprocessed frequency and group delay responses must have high smoothness
• Allows for broad corrective equalization without audible pre-ringing artifacts
• Minimizes the risk of steep over/under correction
• Default full-range distortion must be kept to inaudibly low levels

NEPTUNE is powered by a custom-designed convolution engine and is equipped with several highly optimized and individually tailored FIR corrective filter impulses.
Understanding our Corrective Processing Implementation:

• Audio Input (optional pre-processing with Input Gain Slider)
• Crossfeed Algorithm
• Listening Position to Speakers: 6ft
• Filtered Multichannel Delay Line
• Left Channel Dry Signal
• Left Channel Crossfeed Signal
• Left Channel Dry Signal Copy
• 24db/Oct Low Pass Filter at 1600Hz
• Delay Time: 500μs
• Processed Left Channel Signal Sent to Right Channel
• Right Channel Dry Signal
• Right Channel Crossfeed Signal
• Right Channel Dry Signal Copy
• 24db/Oct Low Pass Filter at 1600Hz
• Delay Time: 500μs
• Processed Right Channel Signal Sent to Left Channel
• Master Quality —> Linear Phase Low Pass FIR Filters
• Zero Latency —> Optimized Minimum Phase Low Pass FIR Filters
• Corrective FIR Filters
• Inverse of Averaged Perceptually Relevant Measurement Impulses
• Full Range (20Hz-20000Hz) Frequency Response Correction
• Full Range (20Hz-20000Hz) Group Delay Correction
• Default Mode applies the default FIR correction filters without additional frequency response or group delay correction
• Adapter Mode applies additional frequency and group delay correction for a specifically tested 3.5mm to 1/4” adapter
• Master Quality —> Linear Phase Low Pass FIR Filters
• Zero Latency —> Optimized Minimum Phase Low Pass FIR Filters
• Audio Output (optional post-processing with Output Gain Slider)

Usage

• NEPTUNE has three basic rules for usage. Let’s walk through them all together.
• RULE ONE: The first rule is that NEPTUNE processing should only be applied when listening on Apple EarPods 3.5mm & AirPods (1st & 2nd Gen) specifically.
• RULE TWO: The second rule is that NEPTUNE should always be the last plugin on your master chain. This is to ensure that all of the audio signal gets processed by the crossfeed and corrective filters. If NEPTUNE is loaded on a mixer channel, only the audio that passes through that specific mixer channel will be processed.
• RULE THREE: The third rule is that NEPTUNE should always be bypassed before exporting. NEPTUNE is a reference plug-in that is specifically meant to simulate a near-perfect studio listening environment. If NEPTUNE is not bypassed, the sonic characteristics specific to Apple EarPods will essentially be embedded into the exported audio.

Note: To bypass NEPTUNE, simply click the Bullseye Audio Logo within the plug-in window or disable it directly in your host DAW.

Frequency Response

The most important quality measure for an audio reproduction system is its frequency response. Ideally, the graphical representation of this would be a perfectly linear response extending from the lowest audible frequency (~20Hz) to the highest (~20kHz). A linear frequency response implies that the amplitudes of all frequencies will perfectly match the source audio. As a point of reference, let’s look at a group of raw, unprocessed frequency response measurements for Apple EarPods.

The frequency response shown in the image above has several features worth mentioning. First and foremost, the response is not flat, with a maximum deviation around 4.5kHz of +22dB and a minimum deviation at 20Hz of -26 dB. These differences will need to be corrected by way of equalization. Fortunately, there are two specific qualities of the response that make it perfectly suited for equalization: smoothness and consistency.

• Frequency response smoothness refers to the rate at which the amplitude changes from a specific frequency to its neighboring frequencies. A high rate of change indicates low smoothness, while a low rate of change indicates high smoothness. In simpler terms, a smooth frequency response will have gradual peaks and troughs, while the opposite will have steep peaks and troughs. The raw frequency response of Apple EarPods is exceptionally smooth, to my knowledge the smoothest of any raw frequency response in the world.
• Frequency response consistency refers to the average deviation of amplitude from the mean of multiple re-seated measurements. A high average deviation from the mean indicates low consistency, while a low average deviation from the mean indicates high consistency. In simpler terms, a consistent frequency response will have minor differences in amplitude over multiple measurements, while the opposite is true of an inconsistent frequency response. The raw frequency response of Apple EarPods is exceptionally consistent.

• High-frequency response smoothness and consistency allow for precise correction filters and a reliable corrected sound output.
• Above are the raw corrected measurements aka the response heard with NEPTUNE processing – Avg: -.9dB from 45Hz – 20kHz

Crossfeed

Crossfeed is the fundamental differentiating factor between headphones and loudspeaker listening. Both headphones and stereo loudspeaker setups alike have two dedicated sound propagation devices that are fed either the left or right-channel audio signal. In simpler terms, there exists a speaker or headphone driver for both the left channel and right channel respectively. The difference between the two systems is that sound from speakers does not travel directly to the eardrum in the same way the sound from headphones (particularly IEMs) does.

The diagram above illustrates how sound travels from each speaker to both ears. Since the direct sound path from each speaker to their associated ear is shorter than the crossfeed sound path, the crossfeed signal has a slight time delay. Our crossfeed is based on the user and both speakers forming an equilateral triangle with a 6ft distance for both direct sound paths and approximately 6.55ft distance for the indirect sound paths with a time delay of 500μs from the direct signal.

It’s important to note that not all of the indirect crossfeed signal reaches the opposite ear. High-frequency sound is directional and does not curve around the head to the same extent as low-frequency sound. The head in this case is essentially acting as a low pass filter of the crossfeed signal (a phenomenon is commonly referred to as the shadow effect of the head). We emulate this by applying a 24db/Oct low pass (FIR linear phase for Master Quality Mode and IIR minimum phase for Zero Latency Mode) filter to each of the crossfeed signals. Below illustrates the perceptual differences between standard headphone listening and headphone listening with crossfeed.

• Why introduce crossfeed into our audio path? Doesn’t crossfeed compromise the integrity of the original signal? Yes, that’s correct actually, it does, but if all stages of the audio production and editing process are influenced by crossfeed (given the effect is consistent enough to reliably program, which is true of crossfeed), then it is an essential feature to replicate to perceive the audio in the way the creators intended to deliver it.
• Crossfeed from speakers is an artifact, it’s not good or bad, it just is and has always been. Since it’s significant enough to modulate our stereo field perceptions, its sonic imprint has embedded itself into nearly all of the audio we listen to daily.

Distortion

• Distortion is a key component of a high-quality audio reproduction system. Distortion can be broadly defined as any additional sound that is not present in the digital waveform. Distortion types include harmonic, inharmonic, noise, and jitter. Each type of distortion can manifest at any point in the audio signal chain, though each type of distortion is commonly linked to specific sources.
• Harmonic and inharmonic distortions are typically produced by loudspeakers or headphone drivers. Noise is primarily introduced by the external environment, which usually exceeds whatever noise is generated by electronic components like DACs, ADCs and amplifiers. Lastly, jitter occurs specifically during digital-to-analog or analog-to-digital conversion and relates to variations in the timing of clock cycle intervals within DACs or ADCs. Modern audio devices typically control jitter to imperceptible levels, residing below the noise floor.
• NEPTUNE in its current form, does not correct for distortion in any way.
• Knowing this, the pair of headphones we chose to correct for required world-class distortion performance out of the box. As seen in the graph below, with weighted distortion values of less than .02% over the majority of the audible frequency range, Apple EarPods have unbelievably good performance in this department.

Time Response

The time response, or group delay, is the final marker of an audio system’s quality. Ideally, the graphical representation of this would be a perfectly linear response extending from the lowest audible frequency (~20Hz) to the highest (~20kHz). A linear group delay response implies that all frequencies will pass through the system at exactly the correct moment in time as instructed by the source audio. As a point of reference, let’s look at a group of raw, unprocessed group delay response measurements for Apple EarPods.

• The group delay response shown in the image above has several features worth mentioning. First and foremost, the response is not flat, with a maximum deviation around 25Hz at +5ms and a minimum deviation at 900Hz of -90μs.
• These differences will need to be corrected by way of equalization. Fortunately, there are two specific qualities of the response that make it perfectly suited for equalization: smoothness and consistency.
• Group delay response smoothness refers to the rate at which the time response changes from a specific frequency to its neighboring frequencies. A high rate of change indicates low smoothness, while a low rate of change indicates high smoothness. In simpler terms, a smooth group delay response will have gradual peaks and troughs, while the opposite will have steep peaks and troughs. The raw group delay response of Apple EarPods is exceptionally smooth, to my knowledge the smoothest of any raw group delay response in the world.
• Group delay response consistency refers to the average deviation of time from the mean of multiple re-seated measurements. A high average deviation from the mean indicates low consistency, while a low average deviation from the mean indicates high consistency. In simpler terms, a consistent group delay response will have minor differences in time over multiple measurements, while the opposite is true of an inconsistent group delay response. The raw group delay response of Apple EarPods is exceptionally consistent

High group delay response smoothness and consistency allow for precise correction filters and a reliable corrected sound output. Above are the raw corrected measurements aka the response heard with NEPTUNE processing – Avg: +24μs from 45Hz-20kHz

Interface

Interface Part 1 of 2

1. Bullseye Audio Logo: Clicking this toggles NEPTUNE processing on and off and color theme from full range color to greyscale
2. NEPTUNE Logo: Clicking this will open the registration or account window
3.  Quality Mode Button: Clicking this will toggle between Master Quality Mode and Zero Latency Mode (note: Master Quality Mode features linear phase FIR filters for both crossfeed and corrective processing while Zero Latency Mode features minimum phase FIR filters for both crossfeed and corrective processing.)
4.  Settings Gear Button: Clicking this toggles between the Quality Mode Button and the Adapter Mode Button
5. Adapter Mode Button: Clicking this will toggle between Default Quality Mode and Adapter Quality Mode (note: Adapter Quality Mode applies additional frequency and group delay correction for a specifically tested 3.5mm to 1/4” adapter)
   • 6a, 6b, 6c – Displays the audio input volume with each large bar representing 24dB increments from -48dB on the right to 0dB on the left, the small white bar on the far left indicates that the audio input is clipping, the raw decibel value for the audio input is the decibel value on the bottom left
   • 6d – Audio Input Gain Slider: Controls the volume of the audio input
   • 7a, 7b & 7c – Displays the audio output volume with each large bar representing 24dB increments from -48dB on the left to 0dB on the right, the small white bar on the far right indicates that the audio output is clipping, the raw decibel value for the audio output is the decibel value on the bottom right
   • 7d – Audio Output Gain Slider: Controls the volume of the audio output

Frequency Data

• Frequency Range: 45Hz – 20kHz —> Max: +22.6dB, Min: -10dB, Avg: +5.1dB

• Frequency Range: 45Hz – 20kHz —> Max: +21.1dB, Min: -10dB, Avg: +5.1dB

• Frequency Range: 45Hz – 20kHz —> Max: +4.2dB, Min: -6dB, Avg: -.9dB

• Frequency Range: 45Hz – 20kHz —> Max: +3.5dB, Min: -5dB, Avg: -.9dB

• Max Correction: -22.6dB, Min Correction: +6.2dB, Avg Correction: +/-4.2dB

• Max Correction: -21.1dB, Min Correction: +5dB, Avg Correction: +/-4.2dB

Group Delay Data

• Frequency Range: 45Hz – 20kHz —> Max: +3.48ms, Min: -220μs, Avg: +735μs

• Frequency Range: 45Hz – 20kHz —> Max: +3.44ms, Min: -130μs, Avg: +685μs

• Frequency Range: 45Hz – 20kHz —> Max: +640μs, Min: -40μs, Avg: +24μs

• Frequency Range: 45Hz – 20kHz —> Max: +692μs, Min: -16μs, Avg: +18μs

• Max Correction: -2.84ms, Min Correction: +142μs, Avg Correction: -710μs

• Max Correction: -2.75ms, Min Correction: +114μs, Avg Correction: -666μs

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