[Sound-open-firmware] EQ component documentation

[Seppo Ingalsuo]

Hi Daniel,

On 21.7.2021 17.40, Daniel Baluta wrote:
> Hi Seppo,
>
> Is there any documentation on how to use the Equalizer component for SOF?
>
> Is there any way to dynamically change the coefficients at runtime?

The documentation is my task list. However there are clear (hope so) 
examples in tools/tune/eq. See first example_iir_eq.m script. It needs 
Octave or Matlab with signal-processing package. The IIR equalizers are 
designed manually with parametric 2nd order blocks. The parameters are 
usually center frequency, Q-value, and gain.

A more complex example is example_fir_eq.m. FIR can be designed 
parametrically with prototype IIR as target response or via a direct 
target response with (frequency, dB magnitude) points. The target can be 
also computed from delta of desired vs. measured frequency response.

The script example_spk_eq.m shows an EQ that combines both IIR and FIR. 
IIR is efficient in coarse shape definition and FIR for very detailed, 
but take care of not going into too small details with it. The FIR 
response can be controlled with octave bands smoothing.

The run-time control of EQs is documented in 
https://thesofproject.github.io/latest/developer_guides/tuning/sof-ctl.html

The equalizers (high-pass for some inputs) those are used currently are 
embedded into topology and do not need runtime setup. See the topology 
CMakeList.txt for examples of embedding them.

Hope this helps to get started!

Cheers,
Seppo


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