Clic-noise for first playback after class initialization

[drtrigon]

I am working on a small project https://github.com/drtrigon/singsang. Thanks a lot for your library as it is very useful and usually working well!

As I implemented recording I need to change I2S config during runtime. ESP32-audioI2S does all the I2S config in the constructor thus I have to destroy and re-create the class.

In the beginning of the first playback I always get a quite strong clic-noise. As I figured out this is most probably related to setting the volume to some non-zero value. I found a work-a-round, as can be seen in drtrigon/singsang@38f5952#diff-10c39dd978ada90e0d090a045c4ae5f51dad010f3b754679e15894c9b93d254bR109
basically what it does is; setting the volume to zero, play any track for some time (100 loop() iterations), stop and the finally set the desired volume:

    // prevent clic-noise when setting volume after init of audio lib (work-a-round)
    m_audio->setVolume(0);
    m_audio->connecttoFS(SPIFFS, "audio-battery.mp3");  // any file available can be used
    for (uint8_t i = 0; i < 100; ++i)  // 50 iterations should be enough, take x2
        m_audio->loop();
    m_audio->stopSong();
    m_audio->setVolume(m_currentVolume);

While this works as expected it feels very much like a work-a-round for some fundamental issue in the library.

I see two possible answers to this issue;

1. May be I am doing something wrong in using your libarary? In this case please tell me how to do it properly as I could not find anything related here or in the docs.
2. Please fix the bug. I can only speculate what it is, may be related to empty buffers or something else?

Thanks and regards

[schreibfaul1]

It is possible that there is still (or random) data in the DMA buffer after the audio object has been created. i2s_zero_dma_buffer() should always be called. Hope this helps.

[tueddy]

Hi Wolle,
I have also heard such noises with audio->setTimeOffset(). Can you see if the same fix can be applied here?

Thank you very much!

[tueddy]

I can confirm that the click-noise when changing the file position has been fixed with the latest commit.
As always, many thanks for the super-fast fix!

[drtrigon]

Thanks a lot for your fast response!

I tried both, replacing my work-a-round by a i2s_zero_dma_buffer() as well as compiling against your commit ca85aca without success. It does not solve the issue for me.

It looks like others had similar issues, confer earlephilhower/ESP8266Audio#406
Especially i2s_config.tx_desc_auto_clear as used in

ESP32-audioI2S/src/Audio.cpp

Line 209 in 961b320

m_i2s_config.tx_desc_auto_clear = true; // new in V1.0.1

was reported to cause issues. However I did not yet had the time to test this...

[drtrigon]

update: I did a naiive try by just setting m_i2s_config.tx_desc_auto_clear = false but this did not help.

[cziter15]

@schreibfaul1

After few hours of digging last evening I've found that m_filterBuff is not initialized with zeroes, which means that it will contain random content after Audio object initialization. The filter will be correctly populated after first sample, which is why you've noise/buzz at first playback.

The solution is to fill this buffer with zeroes from the constructor or maybe even better from the stopSong method
memset(m_filterBuff, 0, sizeof(m_filterBuff));

[cziter15]

@drtrigon It looks like my PR has been merged, please update your library and check if the issue has been resolved

[drtrigon]

@drtrigon It looks like my PR has been merged, please update your library and check if the issue has been resolved

@cziter15: I updated to master and while I did no extensive testing it seems to work now as expected (without the work-a-round mentioned). Thanks a lot for your effort and for pinging me!