posts: Add a section on running autoeq to parametric autoeq

posts/2024-05-07-pipewire-parametric-autoeq.md

@@ -26,11 +26,6 @@ Filter 1: ON PK Fc 20 Hz Gain -1.3 dB Q 2.000
 Filter 2: ON PK Fc 31 Hz Gain -7.0 dB Q 0.500
 Filter 3: ON PK Fc 36 Hz Gain 0.7 dB Q 2.000
 Filter 4: ON PK Fc 88 Hz Gain -0.4 dB Q 2.000
-Filter 5: ON PK Fc 430 Hz Gain 1.6 dB Q 0.700
-Filter 6: ON PK Fc 3200 Hz Gain -1.5 dB Q 0.700
-Filter 7: ON PK Fc 7800 Hz Gain -3.9 dB Q 2.000
-Filter 8: ON PK Fc 13000 Hz Gain -6.7 dB Q 2.000
-Filter 9: ON PK Fc 15000 Hz Gain 9.1 dB Q 0.700
 ```
 
 `Fc` is the frequency, `Gain` is the amount with which the signal gets boosted or attenuated around that frequency. `Q` factor controls the bandwidth around the frequency point. To be more precise, `Q` is the ratio of center frequency to bandwidth. If the center frequency is fixed, the bandwidth is inversely proportional to Q implying that as one raises the Q, the bandwidth is narrowed. Q is by far the most useful tool a parametric EQ offers, allowing one to attenuate or boost a narrow or wide range of frequencies within each EQ band.
@@ -43,6 +38,34 @@ Now, this needs to be converted manually into something which [filter-chain](htt
 
 To simplify this, a simple PipeWire module is implemented which reads a parametric EQ text file like preceding and loads filter chain module while translating the inputs from the text file to what the filter chain module expects.
 
+Before writing the PipeWire module, generate such a parametric equalizer file for a selected headphone and target using [AutoEq](https://github.com/jaakkopasanen/AutoEq). While the web interface at [autoeq.app](https://autoeq.app/) can be used, below section covers how to do this from the command line.
+
+# Automatic headphone equalization
+
+Installation instructions for AutoEq can be found [here](https://github.com/jaakkopasanen/AutoEq?tab=readme-ov-file#installing). Take the example of Beyerdynamic DT1990 headphone and Diffuse Field 5128 target. For brevity sake, what target curve to select and why isn't covered here.
+
+Measurements can be found in [measurements](https://github.com/jaakkopasanen/AutoEq/tree/master/measurements) directory and targets can be found in [targets](https://github.com/jaakkopasanen/AutoEq/tree/master/targets) directory. Note that if measurements aren't available for the selected headphone, earphone, or in-ear monitor, AutoEq can't be used. `oratory1990` and `crinacle` are well known folks in the audiophile community who have provided measurements for various popular headphones and in-ears. `oratory1990`'s measurements are considered below.
+
+Create a results directory `dt1990-results` and then execute the below command.
+
+```bash
+python -m autoeq --input-file="measurements/oratory1990/data/over-ear/Beyerdynamic DT 1990 (balanced earpads).csv" --output-dir="dt1990-results" --target="targets/Diffuse field 5128.csv" --parametric-eq --fs=44100,48000
+```
+
+The results directory `dt1990-results` has the below output.
+
+```bash
+Beyerdynamic DT 1990 (balanced earpads).csv
+Beyerdynamic DT 1990 (balanced earpads).png
+Beyerdynamic DT 1990 (balanced earpads) GraphicEQ.txt
+Beyerdynamic DT 1990 (balanced earpads) ParametricEQ.txt
+README.md
+```
+
+The `Beyerdynamic DT 1990 (balanced earpads) ParametricEQ.txt` file has the parametric equalizer configuration needed which can be given to the PipeWire module discussed next. `README` has some information and recommendation.
+
+Similar process can be followed for in-ear monitors as well.
+
 # Module
 
 A module is a client in a shared library `.so` file which shares a PipeWire context with the loading entity. PipeWire context is an object  which manages all locally available resources. See [here](https://docs.pipewire.org/group__pw__context.html#details).
@@ -63,16 +86,20 @@ The focus is on these two tasks and ignore rest of the ceremony around writing t
 
 # Parsing parametric equalizer configuration
 
-A Parametric EQ configuration generated via *AutoEq* or *Squig*, might look like below. This configuration is converted to match the module args.
+Below is the parametric equalizer configuration that was generated in the second section of this post. This configuration is converted to match the module args.
 
 ```
-Preamp: -2.4 dB
-Filter 1: ON PK Fc 52 Hz Gain 1.0 dB Q 0.600
-Filter 2: ON PK Fc 210 Hz Gain -0.5 dB Q 1.800
-Filter 3: ON PK Fc 390 Hz Gain -0.5 dB Q 1.600
-Filter 4: ON PK Fc 2100 Hz Gain 1.3 dB Q 1.200
-Filter 5: ON PK Fc 3600 Hz Gain -1.7 dB Q 2.000
-Filter 6: ON PK Fc 4900 Hz Gain 3.0 dB Q 2.000
+Preamp: -6.0 dB
+Filter 1: ON LSC Fc 105 Hz Gain -5.2 dB Q 0.70
+Filter 2: ON PK Fc 206 Hz Gain -5.3 dB Q 0.51
+Filter 3: ON PK Fc 4532 Hz Gain 5.5 dB Q 0.41
+Filter 4: ON PK Fc 791 Hz Gain 2.0 dB Q 1.43
+Filter 5: ON PK Fc 6829 Hz Gain -3.8 dB Q 2.04
+Filter 6: ON HSC Fc 10000 Hz Gain 3.1 dB Q 0.70
+Filter 7: ON PK Fc 8944 Hz Gain -1.4 dB Q 2.88
+Filter 8: ON PK Fc 3751 Hz Gain -1.6 dB Q 5.97
+Filter 9: ON PK Fc 4458 Hz Gain 1.5 dB Q 6.00
+Filter 10: ON PK Fc 39 Hz Gain -0.2 dB Q 1.88
 ```
 
 For every line read, a node entry like below is generated.
@@ -95,7 +122,7 @@ When a pre-amp gain is required, which is usually the case when applying EQ, the
   type    = builtin,
   name    = eq_band_1,
   label   = bq_highshelf,
-  control = { Freq = 0, Gain = -2.4, Q = 1.0 },
+  control = { Freq = 0, Gain = -6.0, Q = 1.0 },
 }
 ```
 
@@ -105,8 +132,8 @@ Similarly, for `Filter 1` this would be
 {
   type    = builtin,
   name    = eq_band_2,
-  label   = bq_peaking,
-  control = { Freq = 52, Gain = 1.0, Q = 0.600 },
+  label   = bq_lowshelf,
+  control = { Freq = 105, Gain = -5.2, Q = 0.7 },
 }
 ```