[opus] Periodical noise during DTX

[강인규]

Hi.

I experienced same issue reported in
https://gitlab.xiph.org/xiph/opus/issues/2026


The problem is that there are periodical(400ms) noise during DTX when the
noise changed dramatically.

I have found that the VAD value of silk does not affects to the
DTX decision.

If the background noise suddenly changes(by excessive echo cancellation,
mute on/off operation, etc.) the silk generate a voice activated frame.

Nevertheless, opus keeps the DTX state.

As a result, decoder decode the voice activated frame every 400ms during
DTX.

This causes the periodical noise.


I attached a fixed file.

Please review this.


Thanks,

InGyu Kang
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