Pop/Crack sound at the end

[fraimondo]

I don't know if this is still in active development, but I will leave it here anyway.

I'm currently trying to use an arduino/genuino zero to play wav files from the SD card. I followed the example from the "Arduino Zero Simple audio player". I found to problems:

1. Power/Line/Background noise is very high.
2. Crack/pop sound at the end.

I managed to solve 1 by following the steps in this guide. The more you advance in the guide, the better the noise reduction.

The problem comes with 2. The pop or crack sound at the end might be due to a library issue. So far my tests point out at the DAC having a value different than 0 up to the moment the end function is called. Getting through the code, I can see that the interruptions are enabled when the file starts playing, but if there's no more file to read, then the interruptions keep working until the end function is called. In that interim, the interruption function keeps writing the last buffer read from the file.

Also, as another question: isn't the interruption handler missing the last sample in the buffer each time?

if (__SampleIndex < __NumberOfSamples - 1) {
    analogWrite(A0, __WavSamples[__SampleIndex++]);
}  else {
    __SampleIndex = 0;
}

Since it's a <, it could never be __NumberOfSamples - 1, meaning that the last position in the buffer is never read. Also, in the else case, nothing is written to A0, so the buffer starts from scratch, but a sample is skipped. Of course skipping a sample at that frequency is nothing, it just took me some time to understand how it works.

There are many ways of solving this issue, and since it's blocking my project a bit, I will tacle this issue soon. I'm creating this issue in order to get the opinion from the original coders in case I'm missing something here.

[fraimondo]

Did some debugging:

• The cracking sound came from the metadata. Indeed the example was not taking into account the WAV header and metadata. It was just playing the WAV as it is a RAW PCM. Which is not.
• After several repetitions of playing the same file, the arduino stopped playing. That was due to malloc being called in begin but not free in end. Memory bug.
• Buffer is played continuously after the end of the reading, unless end is called. Which is totally arbitrary since the library has a locking behaviour but s for the file reading only. This has still to be fixed. Function play should not return until the very last sample of the file is written in the DAC.
• File is being closed inside the play function, while it's opened by the caller. To respect normal conventions, caller of open should call close.

See my fix

Works like a charm now. I'm still waiting for some components to see if I can reduce the noise from the amplifier.

[agdl]

@fraimondo what about PR your changes?

[fraimondo]

I went a little bit further with the implementation and added some features

1. Now it takes 10-bit WAV files including header and sets sample rate accordingly.
2. It uses SdFat library (faster)
3. Play method waits until the last sample to return (completely blocking). Previous behaviour was to return after las sample was read.
4. Added a prepare method to read header and initialise the buffer. I needed that a call to play starts playing the file immediately with 0 delay.
5. When there are no more samples in the buffer, a neutral sample is written to the DAC, not a 0.

You can check my implementation here. I prefer to merge and keep one library, but I need this realtime reactivity to the play method.

Let me know what you think. I can update the example also.

[ANDinstruments]

Hello!

I am trying to implement your new version of the audiozero library but I don't understand how to use the new functions? Could you update the example-file?

[fraimondo]

Hi @ANDinstruments

Just updated the example file so you can check how to use it.

Remember that is has to be a mono WAV file, encoded to 10 bits samples.