Runtime Tuning

Runtime tuning of components and pipelines can be achieved using the sof-ctl tool.

The tool is available in SOF repository in directory tools/ctl. It performs runtime IO access using the ext bytes or tlv bytes control of Sound Open Firmware components like eq_iir and eq_fir. This tool is used to upload runtime data to alter the performance or processing characteristsics at runtime of a audio component. e.g Capability to change EQ response in runtime is useful for transducer tuning and for scenario of having equalizers under control of user space service.

This document mainly focuses on examples of the sof-ctl around the EQ FIR and IIR components since the tool was developed alongside these components. The concepts outlined here for EQs will equally applt to other component types that support updating runtime data.

Please find other document(s) in this section how to setup persistently equalizers via topology in boot. There will be also general documentation about IIR and FIR and tuning.

Find out effect numids

To access the right instance the numid of the equalizer needs to be known. As example with topology sof-apl-eq-pcm512x.tplg the numids are as follows:

amixer -Dhw:0 controls | grep EQ
#numid=23,iface=MIXER,name='EQFIR1.0 EQFIR'
#numid=22,iface=MIXER,name='EQIIR1.0 EQIIR'

Therefore to control the IIR instance use numid=22 and to control the FIR EQ instance use numid=23. Note that this depends on topology and varies. In case there are even more equalizers in the topology the numbers x.y in e.g. EQFIR1.0 help to navigate to pipeline and instance number. In this example the equalizers are in the same pipeline 1 in cascade.

Example equalizer settings

This directory contains some simple example setups for convenience. The used file format for txt format files is comma separated unsigned 32 bit decimal integers. Though the files are single line, additional blanks and line feeds are tolerated. The trailing comma seen is not mandatory. The data format for filter coefficients and other embedded control is described in uapi/eq.h.

Creating equalizer configurations requires GNU Octave or Matlab(R) numerical computing software with signal toolbox. The equalizer tuning tool is found in tools/tune/eq directory.

File name Explanation
eq_iir_flat.txt Recursive filter with one as transfer function
eq_iir_bandpass.txt Simple bandpass response
eq_iir_bassboost.txt Simple high-pass and low-shelf
eq_iir_loudness.txt Loudness effect from example_iir_eq.m
File name Explanation
eq_fir_flat.txt One tap filter with coefficient one
eq_fir_mid.txt Simple mid boost response
eq_fir_loudness.txt Loudness effect from example_fir_eq.m

Code to generate IIR and FIR loudness effects is available in in skripts example_iir_eq.m and example_fir_eq.m in SOFT/tune/eq. The flat response generation is also demonstrated in these example. The flat responses are there embedded to previous responses as selectable options to demonstrate the preset EQ capability. However the kernel does not yet support preset switching without re-uploading the whole configuration.

The equalizer can be updated only when SOF is idle. Update during playback is not currently supported (until SOF v1.4) and when attempted the playback will continue with existing setting. The driver will re-send to configuration when DSP is not busy.

E.g. to switch the IIR equalizer to bandpass use command:

sof-ctl -Dhw:0 -n 22 -s eq_iir_bandpass.txt

Succesfull execution will produce next output.

#Applying configuration "eq_iir_bandpass.txt" into device hw:0 control numid=22.
#84,2,1,0,0,2,2,3316150158,2048164275,513807534,3267352229,513807534,0,16384,
#3867454526,1191025347,38870735,77741469,38870735,4294967294,16458
#Success.

After this command the playback sound will have all lowest and highest frequencies suppressed and sound very thin. You may experiment with responses “flat” and “bassboost” to hear other examples of manipulating spectral characteristics of playback audio.

To check what has been applied to DSP the equalizer coefficients can be read back by omitting the -s switch.

sof-ctl -Dhw:0 -n 22
#Retrieving configuration for device hw:0 control numid=22.
#Success.
#84,2,1,0,0,2,2,3316150158,2048164275,513807534,3267352229,513807534,0,16384,
#3867454526,1191025347,38870735,77741469,38870735,4294967294,16458

Help

For completeness the command line options are described with -h switch.

Mail list sound-open-firmware@alsa-project.org is recommended contact for technical discussion about equalizers and tuning.