Custom Parametric Eq

Custom Parametric Eq is the final catch all for all equalizer apps that are not compatible with any of the eq apps covered on autoeq.app. With Custom Parametric Eq you can create any parametric or graphic eq configuration you want. You can add as many filters as your app support and for each filter you can configure the adjustable frequency, gain and quality ranges. What you put into these min and max values should match how small and big numbers you can input into your eq app.

Custom Graphic Equalizer

Custom grahpic equalizers can be created with Custom Parametric Eq by setting both Min Fc and Max Fc to the frequency of the filter (slider) and setting both Min Q and Max Q to the quality (width) of the filter.

Knowing the quality of the filters can be quite tricky with graphic equalizers. You can estimate this based on the frequencies of the filters:

1. Calculate frequency differences for the first two filters in octaves: dFc12 = log2(Fc2 / Fc1), or with natural logarithm: ln(Fc2 / Fc1) / ln(2), where Fc1 is the frequency of the filter number 1 and Fc2 is the frequency of the filter number 2. This is the bandwidth estimate for the first filter.
2. Calculate the same for filters 2 and 3: dFc23 = log2(Fc3 / Fc2).
3. Calculate average of the two: (dFc12 + dFc23) / 2. This is the bandwidth estimate for the second filter.
4. Repeat steps 2 and 3 for each of the parallel filter pairs.
5. Calculate qualities for all of the filters by using Sengpiel Audio's Q - Bandwidth Calculator.

Let's see how this works out for a real example. We'll calculate filter qualities for Spotify's built-in equalizer app. The app has filters with frequencies 60, 150, 400, 1000, 2400, 15000.

First the frequency differences in octaves:

• dFc12 = log2(150 / 60) = 1.32
• dFc23 = log2(400 / 150) = 1.42
• dFc34 = log2(1000 / 400) = 1.32
• dFc45 = log2(2400 / 1000) = 1.26
• dFc56 = log2(15000 / 2400) = 2.64

As we see, most of the gaps are of different size. Makes one think what were the people thinking at Spotify when implementing an equalizer like this...

Next the bandwidths of the filters:

• BW1 = dFc12 = 1.32, we'll use the difference of the first two filters for the first filter.
• BW2 = (dFc23 + dFc12) / 2 = (1.42 + 1.32) / 2 = 1.37, we'll use the average of the two gaps surrounding the second filter.
• BW3 = (dFc34 + dFc23) / 2 = (1.32 + 1.42) / 2 = 1.37
• BW4 = (dFc45 + dFc34) / 2 = (1.26 + 1.32) / 2 = 1.29
• BW5 = (dFc56 + dFc45) / 2 = (2.64 + 1.26) / 2 = 1.95, we will, however, use value of 1.3 for this since the last filter is so far away from all the others that it's likely that the second to last filter isn't so wide.
• BW5 = dFc56 = 2.64

There's of course no guarantees that the actual filter bandwidths are like this, but these are our best estimates.

And finally the qualities with Sengpiel Audio's calculator

• Q1 = 1.06
• Q2 = 1.01
• Q3 = 1.01
• Q4 = 1.08
• Q5 = 1.07
• Q6 = 0.48

Spotify's built-in equalizer allows you to adjust the filter gains between -12dB and +12dB. And with that we have everything we need to create eq optimizer config for Spotify's built-in equalizer:

Peaking
Min Fc: 60, Min Q: 1.06, Min gain: -12
Max Fc: 60, Min Q: 1.06, Min gain: 12

Peaking
Min Fc: 150, Min Q: 1.01, Min gain: -12
Max Fc: 150, Min Q: 1.01, Min gain: 12

Peaking
Min Fc: 400, Min Q: 1.01, Min gain: -12
Max Fc: 400, Min Q: 1.01, Min gain: 12

Peaking
Min Fc: 1000, Min Q: 1.08, Min gain: -12
Max Fc: 1000, Min Q: 1.08, Min gain: 12

Peaking
Min Fc: 2400, Min Q: 1.07, Min gain: -12
Max Fc: 2400, Min Q: 1.07, Min gain: 12

Peaking
Min Fc: 15000, Min Q: 0.48, Min gain: -12
Max Fc: 15000, Min Q: 0.48, Min gain: 12

Easy? Well, no, but this is the last resort that can cover pretty much any possible non-convolution-based equalizer app.