Audio samples don't work on Android

Magnus21

Hello, so my app records audio and does audio processing on it.

It works perfectly on Desktop, but on Mobile I don't seem to get any correct floating point audio samples.
I use a chart to show the value of all samples and the Android version seems to only receive values of value 0 and negative values, but nothing that makes sense.

Here are screenshots of what I mean:
Desktop screenshot
As you can see, on Desktop the audio samples are good.

However, on mobile I only get weird values (values <= 0):
Mobile screenshot

When I try the audio example app from Qt, that does similar audio processing, I get correct samples on Android as well. But this example app uses integer samples. I need the floating point samples though.

Here is my code for setting up the audio recording:

m_format.setSampleRate(SAMPLE_RATE);
// mono sound
m_format.setChannelCount(1);
// aubio requires float
m_format.setSampleType(QAudioFormat::SampleType::Float);
// floats have a size of 32 bit
m_format.setSampleSize(sizeof(float) * 8);
m_format.setCodec("audio/pcm");
m_rec = new QAudioInput(m_format, this);

Any idea what could be wrong with floating point samples on Android?

If you need the full source code, it's available here: https://github.com/magnus-gross/quickpitch

Magnus21

OK, I found the problem. Qt doesn't support float samples on Android at all and changes the format to integer samples, even if you explicitly specify floating point samples. The QAudioDeviceInfo provides a isFormatSupported method to check for these cases.

I now proceeded to write a int to float conversion method and it works well now.