README.md

AutoEQ

TL;DR If you are here just looking to make your headphones sound better, find your headphone model in here or here and follow instructions in Usage section.

About This Project

AutoEQ is a project for equalizing headphone frequency responses automatically and it achieves this by parsing frequency response measurements and producing a equalization settings which correct the headphone to a neutral sound. This project currently has 700+ onear headphones covered in the results folder. Results are organized by target/source/type/headphone so a Sennheiser HD 650 measured by Innerfidelity and tuned to Innerfidelity 2017 compensation curve would be found in Innerfidelity 2017/innerfidelity/onear/Sennheiser HD 650. See Usage for instructions how to use the results with EqualizerAPO and Results for details about parameters and how the results were obtained.

AutoEQ is not just a collection of automatically produced headphone equalization settings but also a tool for equalizing headphones for yourself. frequency_response.py provides methods for reading data, equalizing it to a given target response and saving the results for usage with EqualizerAPO. It's possible to use different compensation (target) curves, apply tilt for making the headphones brighter/darker and adding a bass boost. It's even possible to make one headphone sound (roughly) like another headphone. For more info about equalizing see Equalizing

Third major contribution of this project is the measurement data, compensation curves and calibration curves all in a numerical format. Everything is stored as CSV files so they are easy to process with any programming language or even Microsoft Excel. See Calibration and Data Processing for more technical description about how things were obtained and processed.

Sennheiser HD 650 equalization results plotted

Usage

Equalization settings produced by AutoEQ are EqualizerAPO GraphicEQ configuration lines, one for each headphone processed. They look like this:

GraphicEQ: 10 -84; 20 6.0; 22 6.0; 23 6.0; 25 6.0; 26 5.9; 28 5.6; 30 5.3; 32 4.8; 35 4.3; 37 3.9; 40 3.5; 42 3.3; 45 3.0; 49 2.7; 52 2.6; 56 2.5; 59 2.1; 64 1.8; 68 1.9; 73 2.2; 78 1.7; 83 0.9; 89 0.3; 95 -0.2; 102 -0.7; 109 -1.1; 117 -1.5; 125 -1.9; 134 -2.2; 143 -2.5; 153 -2.6; 164 -2.5; 175 -2.5; 188 -2.6; 201 -2.7; 215 -2.5; 230 -2.4; 246 -2.3; 263 -2.2; 282 -2.0; 301 -1.9; 323 -1.8; 345 -1.5; 369 -1.5; 395 -1.4; 423 -1.2; 452 -1.0; 484 -1.0; 518 -1.0; 554 -0.8; 593 -0.5; 635 -0.4; 679 -0.5; 726 -0.3; 777 -0.2; 832 -0.4; 890 -0.6; 952 -0.4; 1019 -0.1; 1090 -0.5; 1167 -0.8; 1248 -1.0; 1336 -1.1; 1429 -1.3; 1529 -1.3; 1636 -1.6; 1751 -1.6; 1873 -1.4; 2004 -0.9; 2145 -0.7; 2295 -0.5; 2455 -0.2; 2627 0.1; 2811 -0.1; 3008 -0.6; 3219 -1.1; 3444 -1.0; 3685 -0.6; 3943 0.0; 4219 -0.0; 4514 -0.1; 4830 0.9; 5168 3.8; 5530 5.9; 5917 5.2; 6331 4.4; 6775 3.9; 7249 1.3; 7756 0.3; 8299 0.0; 8880 0.0; 9502 0.0; 10167 0.0; 10879 0.0; 11640 0.0; 12455 0.0; 13327 0.0; 14260 0.0; 15258 0.0; 16326 0.0; 17469 0.0; 18692 0.0; 20000 0.0

Plain EqualizerAPO

Simplest way is to install EqualizerAPO and edit configuration file in C:\Program Files\EqualizerAPO\config\config.txt. Disable Include: example.txt, replace GraphicEQ: ... line with the one found in results and set Preamp: .... Using Sennheiser HD 650 would make config file look like this:

Preamp: -6 dB
# Include: example.txt
GraphicEQ: 10 -84; 20 6.0; 22 6.0; 23 6.0; 25 6.0; 26 5.9; 28 5.6; 30 5.3; 32 4.8; 35 4.3; 37 3.9; 40 3.5; 42 3.3; 45 3.0; 49 2.7; 52 2.6; 56 2.5; 59 2.1; 64 1.8; 68 1.9; 73 2.2; 78 1.7; 83 0.9; 89 0.3; 95 -0.2; 102 -0.7; 109 -1.1; 117 -1.5; 125 -1.9; 134 -2.2; 143 -2.5; 153 -2.6; 164 -2.5; 175 -2.5; 188 -2.6; 201 -2.7; 215 -2.5; 230 -2.4; 246 -2.3; 263 -2.2; 282 -2.0; 301 -1.9; 323 -1.8; 345 -1.5; 369 -1.5; 395 -1.4; 423 -1.2; 452 -1.0; 484 -1.0; 518 -1.0; 554 -0.8; 593 -0.5; 635 -0.4; 679 -0.5; 726 -0.3; 777 -0.2; 832 -0.4; 890 -0.6; 952 -0.4; 1019 -0.1; 1090 -0.5; 1167 -0.8; 1248 -1.0; 1336 -1.1; 1429 -1.3; 1529 -1.3; 1636 -1.6; 1751 -1.6; 1873 -1.4; 2004 -0.9; 2145 -0.7; 2295 -0.5; 2455 -0.2; 2627 0.1; 2811 -0.1; 3008 -0.6; 3219 -1.1; 3444 -1.0; 3685 -0.6; 3943 0.0; 4219 -0.0; 4514 -0.1; 4830 0.9; 5168 3.8; 5530 5.9; 5917 5.2; 6331 4.4; 6775 3.9; 7249 1.3; 7756 0.3; 8299 0.0; 8880 0.0; 9502 0.0; 10167 0.0; 10879 0.0; 11640 0.0; 12455 0.0; 13327 0.0; 14260 0.0; 15258 0.0; 16326 0.0; 17469 0.0; 18692 0.0; 20000 0.0

EqualizerAPO has a graphical user interface for adjusting configurations. Launch the editor from C:\Program Files\EqualizerAPO\Editor.exe.

EqualizerAPO Editor GUI

HeSuVi

HeSuVi is GUI for EqualizerAPO which has almost all headphone surround virtualizations available. HeSuVi also provides a convenient graphical user interface for adjusting the equalizer, toggling eq on and off, adjusting preamp and saving and restoring multiple different configurations making it very easy to compare different eq settings. To load an eq into HeSuVi, close HeSuVi and replace contents of HeSuVi's eq file C:\Program Files\EqualizerAPO\config\HeSuVi\eq.txt with the produced GraphicEQ: ... line. Then start HeSuVi and adjust global volume for both channels to highest eq value. You can save the configuration with profile manager in bottom right corner.

HeSuVi GUI for EqualizerAPO

Peace

If you are already using Peace GUI for EqualizerAPO you'll have to disable the configurations made by it because Peace doesn't work with GraphicEQ and you don't want to have two EQs on at the same time. Simply toggling the master switch in the top right corner off will disable everything Peace is doing. After Peace has been disabled you can follow instructions in the Plain EqualizerAPO section.

Peace GUI for EqualizerAPO with master switch off

Producing parametric eq settings for Peace users could be a consideration for the future if enough people request that.

Results

The main princible used by AutoEQ for producing the equalization function is to invert error function. Error is the difference between raw microphone data and the compensation (target) curve. If headphone's frequency response is 4 dB below the target at 20 Hz equalization function will have +4 dB boost at 20 Hz. In reality simply inverting the error is not sufficient since measurements and equalization have several problems that need to be addressed, see Technical Challenges for more details.

Results provided in this project have all the on-ear headphone measurements from Innerfidelity and Headphone.com with 4 different target responses:

• Modified version of Innerfidelity target by @Serious user on Super Best Audio Friends forum
• Innerfidelity 2017
• Headphone.com
• Sonoma Model One measurement by Innerfidelity

All but the Headphone.com compensation curve are targeted to Innerfidelity measurements. But all targets have results also for Headphone.com data, in these cases the Headphone.com data was calibrated to Innerfidelity measurement system before applying the compensation.

Recommended compensation curve is the modified version of Innerfidelity target curve produced by Serious user on Super Best Audio Friends forum. This curve doesn't have the glaring problems but is quite well balanced overall. Curve was turned into a compensation for raw microphone data and tilted 0.2 dB / octave brighter. See the forum thread for discussion about the original target. innerfidelity/resources/innerfidelity_compensation_SBAF-Serious-brighter.csv

Innerfidelity 2017 compensation curve is the result of Tyll Hertsens calibrating his measurement head on the Harman reference listening room and is a significant improvement over the old compensation curve used in PDFs. However 2017 curve seems to underestimate 2 to 5 kHZ region by several dB leading the equalization to boost those frequencies too much. innerfidelity/resources/innerfidelity_compensation_2017.csv

Headphone.com compensation curve is used by Headphone.com with their Frequency Response graphs but this seems to underestimate treble even more than the 2017 Innerfidelity curve leading to even brighter equalization. headphonecom/resources/headphonecom_compensation.csv

Fourth target is the raw measurement data of Sonoma Model One headphone system as measured by Innerfidelity. This is an experiment in equalizing headphones to sound like other headphones. Sonoma Model One is reasonably neutrally tuned headphone and as such works as a quite good equalization target. I personally prefer the modified SBAF-Serious target though. innerfidelity/data/onear/Sonoma Model One/Sonoma Model One.csv

None of these targets have bass boost seen in Harman target responses and therefore a +4dB boost was applied for all results. Above 6 to 8kHz data is filtered more heavily to avoid measurement artifacts and no positive gain (boost) is applied. In the upper treble measurements are less reliable and boosting them too much will cause serious problem while having some narrow dips is not a problem at all.

Equalizing

frequency_response.py is the tool used to produce the equalization results from measurement data. There is no fancy graphical user interface but instead it is used from command line.

Installing

• Download AutoEQ zip and exctract to a convenient location.
• Download and install Python3. Make sure to check Install Python3 to PATH
• Install virtualenv. Run this on command prompt. Search cmd in Windows start menu.

pip install virtualenv

• Go to AutoEQ location

cd C:\path\to\AutoEq-master

• Create virtual environment

virtualenv venv

• Activate virtualenv

.\venv\scripts\activate

• Install required packages

pip install -r requirements.txt

• Verify installation

python frequency_response.py -H

When coming back at a later time you'll only need to activate virtual environment again

cd C:\path\to\AutoEq-master
.\venv\scripts\activate

Command Line Arguments

usage: frequency_response.py [-h] --input_dir INPUT_DIR --output_dir
                             OUTPUT_DIR [--calibration CALIBRATION]
                             [--compensation COMPENSATION] [--equalize]
                             [--bass_boost BASS_BOOST] [--tilt TILT]
                             [--max_gain MAX_GAIN]
                             [--treble_f_lower TREBLE_F_LOWER]
                             [--treble_f_upper TREBLE_F_UPPER]
                             [--treble_max_gain TREBLE_MAX_GAIN]
                             [--treble_gain_k TREBLE_GAIN_K] [--show_plot]

optional arguments:
  -h, --help            show this help message and exit
  --input_dir INPUT_DIR
                        Path to input data directory. Will look for CSV files
                        in the data directory and recursively in sub-
                        directories.
  --output_dir OUTPUT_DIR
                        Path to results directory. Will keep the same relative
                        paths for files foundin input_dir.
  --calibration CALIBRATION
                        File path to CSV containing calibration data. See
                        `calibration` directory.
  --compensation COMPENSATION
                        File path to CSV containing compensation curve.
                        Compensation is necessary when equalizing because all
                        input data is raw microphone data. See
                        innerfidelity/resources and headphonecom/resources.
                        Defaults to "innerfidelity\resources\innerfidelity_com
                        pensation_SBAF-Serious.brighter.csv"
  --equalize            Will run equalization if this parameter exists, no
                        value needed.
  --bass_boost BASS_BOOST
                        Target gain for sub-bass in dB. Has flat response from
                        20 Hz to 60 Hz and a sigmoid slope down to 200 Hz.
                        Defaults to 0.0
  --tilt TILT           Target tilt in dB/octave. Positive value (upwards
                        slope) will result in brighter frequency response and
                        negative value (downwards slope) will result in darker
                        frequency response. 1 dB/octave will produce nearly 10
                        dB difference in desired value between 20 Hz and 20
                        kHz. Tilt is applied with bass boost and both will
                        affect the bass gain. Defaults to 0.0
  --max_gain MAX_GAIN   Maximum positive gain in equalization. Higher max gain
                        allows to equalize deeper dips in frequency response
                        but will limit output volume if no analog gain is
                        available because positive gain requires negative
                        digital preamp equal to maximum positive gain.
                        Defaults to 6.0
  --treble_f_lower TREBLE_F_LOWER
                        Lower bound for transition region between normal and
                        treble frequencies. Treble frequencies can have
                        different smoothing, max gain and gain K. Defaults to
                        6000.0
  --treble_f_upper TREBLE_F_UPPER
                        Upper bound for transition region between normal and
                        treble frequencies. Treble frequencies can have
                        different smoothing, max gain and gain K. Defaults to
                        8000.0
  --treble_max_gain TREBLE_MAX_GAIN
                        Maximum positive gain for equalization in treble
                        region. Defaults to 0.0
  --treble_gain_k TREBLE_GAIN_K
                        Coefficient for treble gain, affects both positive and
                        negative gain. Useful for disabling or reducing
                        equalization power in treble region. Defaults to 1.0.
  --show_plot           Plot will be shown if this parameter exists, no value
                        needed.

Examples

Equalizing Sennheiser HD 650 and saving results to myresults/HD650:

python frequency_response.py --input_dir="innerfidelity\data\onear\Sennheiser HD 650" --output_dir="myresults\HD650" --compensation="innerfidelity\resources\innerfidelity_compensation_SBAF-Serious-brighter.csv" --equalize --bass_boost=4 --show_plot

Equalizing Beyerdynamic DT990 without saving results

python frequency_response.py --input_dir="headphonecom\data\onear\Beyerdynamic DT990" --compensation="headphonecom\resources\headphonecom_compensation.csv" --equalize --bass_boost=4 --show_plot

Equalizing Beyerdynamic DT990 to SBAF-Serious-brighter target. This target is made for Innerfidelity measurements so we need to calibrate Headphone.com measurement.

python frequency_response.py --input_dir="headphonecom\data\onear\Beyerdynamic DT990" --compensation="innerfidelity\resources\innerfidelity_compensation_SBAF-Serious-brighter.csv" --calibration="calibration\headphonecom_raw_to_innerfidelity_raw.csv" --equalize --bass_boost=4 --show_plot

Equalizing all Headphone.com on-ear headphones and saving results to results\onear\SBAF-Serious-brighter\headphonecom. There is a lot of headphones and we don't want to inspect all visually so we'll omit --show_plot

python frequency_response.py --input_dir="headphonecom\data\onear" --output_dir="results\onear\SBAF-Serious-brighter\headphonecom" --compensation="innerfidelity\resources\innerfidelity_compensation_SBAF-Serious-brighter.csv" --calibration="calibration\headphonecom_raw_to_innerfidelity_raw.csv" --equalize --bass_boost=4

Equalizing Beyerdynamic DT 770 to sound like HiFiMAN HE400S. 80ohm version of DT 770 is only available in Headphone.com measurements and HE400S only in Innerfidelity measurements so we'll use calibration once again. To make the bass sound the same we'll set bass boost to zero.

python frequency_response.py --input_dir="headphonecom\data\onear\Beyerdynamic DT770" --compensation="innerfidelity\data\onear\HiFiMAN HE400S\HiFiMAN HE400S.csv" --calibration="calibration\headphonecom_raw_to_innerfidelity_raw.csv" --equalize --bass_boost=0 --show_plot

Viewing HiFiMAN HE400S raw microphone data

python frequency_response.py --input_dir="innerfidelity\data\onear\HiFiMAN HE400S" --show_plot

Feel free to experiment more.

More Data!

If data for you headphone cannot be found in this project but you have an image of the frequency response you might be able to use https://apps.automeris.io/wpd/ to parse the image. You'll have replace all commas , in the produced file with point . and semi-colons ; with comma , in this order. You can you for example Notepad++ for this, just hit Ctrl+h

Calibration

Innerfidelity and Headphone.com have different kind of measurement systems and since there is no any kind of standard calibration for headphone frequency response measurements the data produced by these systems are not directly compatible with each other. Same individual headphone will measure differently in the two systems. This actually applies for all of the existing measurement systems.

To have comparable equalization results and to be able to use all compensation curves for both measurements a calibration was done. Calibration made is not as reliable as a real calibration where a set of reference headphones are measured on both systems and outputs compared but instead a same headphone models but different individual units were used. All headphones with same name were selected from Headphone.com measurement database and Innerfidelity measurement database and results were compared model-wise. Final calibration curve was produced by averaging all the measurement pairs and smoothing the averaged curve. This method is problematic because there are large differences between individual headphones due to manufacturing and placement on the measurement head. Standard deviation is quite high about 5dB at 20Hz but still it's probably closer to truth than not using any calibration at all.

Pictured data is for calibrating Headphone.com measurement to Innerfidelity measurement or in other words estimating how an individual headphone measured by Headphone.com would look like if it was measured by Innerfidelity. When using calibration data in frequency_response.py the curve is subtracted for raw data.

Warning Using calibration will change the saved raw data and therefore when loading the result a new calibration must not be applied!

Technical Challenges

Simply inverting headphone frequency response deviation from target response does not usually produce sufficient results. Some problems are caused by imperfections in measurements, some are reliability issues and some are practical end-user problems. Rtings has a good video on Youtube about measurement system challenges and solutions which is definitely worth checking out. Innerfidelity also has a very educational video on Youtube about measurments and what constitutes as a neutral sound. Main takeoffs are that bass and treble measurements are very inconsistent, neutral sound is not very well defined yet and on-ear headphones have big reliability problems in 8 to 9kHz range due to resonances which move when headphone placement is changed. Harman international has done some solid research into preferred headphone frequency response but since that research was done on a different measurement system the target does not apply directly to Innerfidelity (Summer 2018) and Headphone.com measurements.

There is very little that can be done for fighting bass inconsistencies because the same problems will be there whether equalization is used or not. Headphones simply have different bass responses on different listeners (heads). Therefore bass is taken as is in AutoEQ and equalized as if there was nothing wrong with it. You're mileage may wary. Luckily bass has smaller impact on music and having too much bass (especially sub-bass) doesn't create problems of the same magnitude as having too much treble.

Moving resonances around 8 to 9kHZ may cause big problems if not taken into account. Spikes and dips in this range are of great amplitude and very narrow. If one equalizes these spikes and dips according to frequency response measurement in worst case scenario a spike will move in a place of dip when headphone is moved and therefore the spike is amplified significantly leading to very sharp and piercing sound signature. To counter these problems by default AutoEQ uses heavy smoothing and limited positive gain above 6 to 8kHz. This way the equalization will follow a broader trend of the region and will not care so much about narrow spikes and dips. Also positive gain is limited to 0dB as an extra safety measure against amplifying moved spike. Suppressing a narrow dip even further is not an optimal thing to do but in practice has little negative effect on the sound. Both of these measures will also alleviate upper treble measurement inconsistencies above 11 to 12 kHz.

A practical end-user problem is if too high positive gain is allowed which asks for equal amount of negative digital pre-amp to prevent clipping. This negative preamp will limit maximum volume produced by the system if there is no analog gain available. If a dedicated headphone amplifier is available or if the motherboard/soundcard can drive the headphones loud enough even when using high negative preamp larger --max_gain values can be uses. By default --max_gain is set to +6dB to not to cripple user's volume too much. Max gain will clip the equalization curve which produces sharp kinks in it. Sharp changes in equalization may produce unwanted equalization artifacts. To counter this AutoEQ rounds the corners whenever max gain clips the curve.

Data Processing

Measurement data for this project was obtained by crawling Innerfidelity and Headphone.com databases. For Innerfidelity that means downloading all PDFs, turning them into images with Ghostscript, parsing images with Python PIL package and saving the numerical data. Numerical data obtained this way is an average of the blue and red curves in the frequency response. These curves have been compensated with the old compensation curve which does not match human perception at all. The old compensation curve was then applied in inverse to turn the compensated data into raw microphone data. This raw microphone data is stored in innerfidelity/data. On-ear, in-ear and ear-bud data is separated because they ask for different AutoEQ parameters.

Headphone.com measurements were downloaded as images, both raw and compensated data. Images were parsed into numerical format and raw data saved to headphonecom/data. Both datas were used to obtain Headphone.com compensation curve by calculating differences between raw and compensated data.

Data processing tools are not meant as a user friendly and robust software but instead to be able to be ran once to obtain the raw data.