Tools: Topology2: Swap gain and eqiir in DMIC capture #9700
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An example of this is in the plot below. The recordings were done with sof-hda-generic-2ch.tplg with simulating very loud sound by rubbing the microphone ports in notebook lid (no yelling in home office :) . The upper plot is before and and lower after this change. In upper with amplifying IIR the peaks are clipped to max. PCM codes and then brought down with volume set to -10 dB. In lower plot with proposed topology change the capture is more linear with no saturated intermediate PCM codes values.
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singalsu
commented
Dec 2, 2024
This patch swaps the order of IIR and gain components in capture pipeline. In IPC4 systems the gain component can only attenuate the signal, largest gain is 0 dB (pass-through). The IIR component can be set up to amplify the signal by e.g. +20 dB that is currently default in many topologies. The gain can possibly distort the signal in loud environment. With current "dai-copier -> eqiir -> gain -> module-copier" topology the user configurable gain (ALSA mixer control) can't prevent clipping of audio signal in IIR. While with swapped order "dai-copier -> gain -> eqiir -> module-copier" using attenuation in gain component can be used to prevent audio signal clipping in IIR. It would be useful in capturing audio in a very loud environment. Since the pipeline is 32-bits there is no practical loss of audio quality even if there would be first attenuation and then gain. Plus normally the gain control for Dmic0 is set to maximum. Signed-off-by: Seppo Ingalsuo <[email protected]>
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lgirdwood
reviewed
Dec 2, 2024
lgirdwood
approved these changes
Dec 3, 2024
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SOFCI TEST |
kv2019i
approved these changes
Dec 3, 2024
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Unrelated CI failure for pause and alsabat on LNL |
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This patch swaps the order of IIR and gain components in capture pipeline. In IPC4 systems the gain component can only attenuate the signal, largest gain is 0 dB (pass-through). The IIR component can be set up to amplify the signal by e.g. +20 dB that is currently default in many topologies. The gain can possibly distort the signal in loud environment.
With current "dai-copier -> eqiir -> gain -> module-copier" topology the user configurable gain (ALSA mixer control) can't prevent clipping of audio signal in IIR. While with swapped order "dai-copier -> gain -> eqiir -> module-copier" using attenuation in gain component can be used to prevent audio signal clipping in IIR. It would be useful in capturing audio in a very loud environment.
Since the pipeline is 32-bits there is no practical loss of audio quality even if there would be first attenuation and then gain. Plus normally the gain control for Dmic0 is set to maximum.