Square wave with int32 dtype not working as expected

[ANickerson]

If you create a numpy array with only intmax (2147483647) and play this file, the result is static.

If you convert to float (by dividing by intmax) then a square wave is produced

import sounddevice as sd
import numpy as np
square = np.ones(44100, dtype="int32") * 2147483647
sd.play(square) # Results in static

square_floats = np.ones(44100, dtype="float32")
sd.play(square_floats) # results in "on" state

I would expect these to act the same, is there any reason why they don't? Is there some sort of overflow?

[mgeier]

Oh, that's interesting. It works fine for me on Linux/ALSA. However, if I try it on Linux/OSS, I'm indeed hearing static noise!

What host API are you using?

Theoretically, using 'int32' should be fully supported. The supported types are listed in sd._sampleformats. If the type isn't in there, play() will throw an exception.

[ANickerson]

Yes, I thought it was a bit odd.

I am (unfortunately) using windows7 x64 in this instance.

Fantastic api by the way!

[mgeier]

Well thank you very much!

I fear I can't do anything about the problem from the Python side, this may actually be a problem with PortAudio, and more specifically a certain Windows host API.
Which host API are you using?

You could try to ask about this on the PortAudio mailing list (http://portaudio.com/contacts.html).

It would be good to check if this also happens with a minimal example implemented in C.

[mgeier]

If you have a C compiler at hand, you could test this example:

intmax.c:

#include <stdio.h>
#include <unistd.h>
#include <portaudio.h>

PaDeviceIndex device = 0;
PaTime latency = 0.1;
unsigned long blocksize = 0;
double samplerate = 48000.0;
PaSampleFormat format = paInt32;
int channels = 1;

int callback(const void *input, void *output, unsigned long frame_count
  , const PaStreamCallbackTimeInfo* t, PaStreamCallbackFlags f, void* u)
{
  int* out = output;
  while (frame_count--) { *out++ = 2147483647; }
  if (f) { printf("xrun\n"); }
  return paContinue;
}

int main()
{
  PaError err = Pa_Initialize();
  if (err != paNoError) {
    printf("PortAudio error (init): %s\n", Pa_GetErrorText(err)); return 1;
  }
  PaStreamParameters out = { device, channels, format, latency, NULL };
  PaStream* s = NULL;
  err = Pa_OpenStream(&s, NULL, &out, samplerate, blocksize, 0, callback, NULL);
  if (err != paNoError) {
    printf("PortAudio error (open): %s\n", Pa_GetErrorText(err)); return 1;
  }
  err = Pa_StartStream(s);
  if (err != paNoError) {
    printf("PortAudio error (start): %s\n", Pa_GetErrorText(err)); return 1;
  }
  sleep(5);
  return 0;
}

Makefile:

LDLIBS = -lportaudio

intmax:

I guess make doesn't exist on Windows, you'll have to use whatever is used there to compile the example.
Just change the device variable to your device.

I could reproduce the static noise on the OSS host API with this. It works fine with paFloat32 BTW.

If you can reproduce the error, too, you could send this little example to the PortAudio mailing list.

[mgeier]

@ANickerson Did you try this?