5.1 Channels with PortAudio

Question

I am trying to get started with PortAudio. I am able to build the bundled example file "paex_sine.c" with no problems. This a sine wave on the left channel and a different frequency sine wave on the right channel. This works properly with no errors.

My setup is a 32-bit PC running Puppy Linux Slacko 5.5. It has a SoundBlaster SB0200 with EMU10k1x chip. The Alsa library is v1.0.26, and driver is v1.0.24. I have tested all 5.1 channels using this command:

% speaker-test -Dplug:surround51 -c6

The test plays sound properly on each of the 6 channels, though it does complain about broken pipes. This is probably because the buffer is not large enough in the test program for all 6 channels.

The issue that I am having is that when I modify "paex_sine.c" to run on 6 channels instead of just 2, it will only play sound through the front-right and front-left channels. There are no errors reported, and the 2 channels sound like they should. I have heard that channels must be unmuted in some cases. In AlsaMixer and Puppy's "Retrovol" (which mirrors AlsaMixer), I have set Master, PCM, and Surround to max volume, unmuted. Could there be a mixer in PortAudio that I also have to unmute? I can go back and forth between running speaker-test properly and running the modified paex_sine example and hearing only 2 channels. Here is paex_sine.c that I have modified:

    /** @file paex_sine.c
        @ingroup examples_src
        @brief Play a sine wave for several seconds.
        @author Ross Bencina <[email protected]>
        @author Phil Burk <[email protected]>
    */
    /*
     * $Id: paex_sine.c 1752 2011-09-08 03:21:55Z philburk $
     *
     * This program uses the PortAudio Portable Audio Library.
     * For more information see: http://www.portaudio.com/
     * Copyright (c) 1999-2000 Ross Bencina and Phil Burk
     *
     * Permission is hereby granted, free of charge, to any person obtaining
     * a copy of this software and associated documentation files
     * (the "Software"), to deal in the Software without restriction,
     * including without limitation the rights to use, copy, modify, merge,
     * publish, distribute, sublicense, and/or sell copies of the Software,
     * and to permit persons to whom the Software is furnished to do so,
     * subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be
     * included in all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
     * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
     * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
     * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
     * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
     */

    /*
     * The text above constitutes the entire PortAudio license; however, 
     * the PortAudio community also makes the following non-binding requests:
     *
     * Any person wishing to distribute modifications to the Software is
     * requested to send the modifications to the original developer so that
     * they can be incorporated into the canonical version. It is also 
     * requested that these non-binding requests be included along with the 
     * license above.
     */
    #include <stdio.h>
    #include <math.h>
    #include "portaudio.h"

    #define NUM_SECONDS   (30)
    #define SAMPLE_RATE   (44100)
    #define FRAMES_PER_BUFFER  (192)//(64)

    #ifndef M_PI
    #define M_PI  (3.14159265)
    #endif

    #define TABLE_SIZE   (200)
    typedef struct
    {
        float sine[TABLE_SIZE];
        int left_phase;
        int right_phase;
        int left2_phase;
        int right2_phase;
        int left3_phase;
        int right3_phase;
        char message[20];
    }
    paTestData;

    /* This routine will be called by the PortAudio engine when audio is needed.
    ** It may called at interrupt level on some machines so don't do anything
    ** that could mess up the system like calling malloc() or free().
    */
    static int patestCallback( const void *inputBuffer, void *outputBuffer,
                                unsigned long framesPerBuffer,
                                const PaStreamCallbackTimeInfo* timeInfo,
                                PaStreamCallbackFlags statusFlags,
                                void *userData )
    {
        paTestData *data = (paTestData*)userData;
        float *out = (float*)outputBuffer;
        unsigned long i;

        (void) timeInfo; /* Prevent unused variable warnings. */
        (void) statusFlags;
        (void) inputBuffer;

        for( i=0; i<framesPerBuffer; i++ )
        {
            *out++ = data->sine[data->left_phase];  /* left */
            *out++ = data->sine[data->right_phase];  /* right */
            *out++ = data->sine[data->left2_phase];  /* left */
            *out++ = data->sine[data->right2_phase];  /* right */
            *out++ = data->sine[data->left3_phase];  /* left */
            *out++ = data->sine[data->right3_phase];  /* right */
            data->left_phase += 1;
            if( data->left_phase >= TABLE_SIZE ) data->left_phase -= TABLE_SIZE;
            data->right_phase += 3; /* higher pitch so we can distinguish left and right. */
            if( data->right_phase >= TABLE_SIZE ) data->right_phase -= TABLE_SIZE;
            data->left2_phase += 5;
            if( data->left2_phase >= TABLE_SIZE ) data->left2_phase -= TABLE_SIZE;
            data->right2_phase += 7; /* higher pitch so we can distinguish left and right. */
            if( data->right2_phase >= TABLE_SIZE ) data->right2_phase -= TABLE_SIZE;
            data->left3_phase += 9;
            if( data->left3_phase >= TABLE_SIZE ) data->left3_phase -= TABLE_SIZE;
            data->right3_phase += 11; /* higher pitch so we can distinguish left and right. */
            if( data->right3_phase >= TABLE_SIZE ) data->right3_phase -= TABLE_SIZE;
        }

        return paContinue;
    }

    /*
     * This routine is called by portaudio when playback is done.
     */
    static void StreamFinished( void* userData )
    {
       paTestData *data = (paTestData *) userData;
       printf( "Stream Completed: %s\n", data->message );
    }

    /*******************************************************************/
    int main(void);
    int main(void)
    {
        PaStreamParameters outputParameters;
        PaStream *stream;
        PaError err;
        paTestData data;
        int i;


        printf("PortAudio Test: output sine wave. SR = %d, BufSize = %d\n", SAMPLE_RATE, FRAMES_PER_BUFFER);

        /* initialise sinusoidal wavetable */
        for( i=0; i<TABLE_SIZE; i++ )
        {
            data.sine[i] = (float) sin( ((double)i/(double)TABLE_SIZE) * M_PI * 2. );
        }
        data.left_phase = data.right_phase = 0;
        data.left2_phase = data.right2_phase = 0;
        data.left3_phase = data.right3_phase = 0;

        err = Pa_Initialize();
        if( err != paNoError ) goto error;

        outputParameters.device = Pa_GetDefaultOutputDevice(); /* default output device */
        if (outputParameters.device == paNoDevice) {
          fprintf(stderr,"Error: No default output device.\n");
          goto error;
        }
        outputParameters.channelCount = 6;       /* 5.1 Channel Output */
        outputParameters.sampleFormat = paFloat32; /* 32 bit floating point output */
        outputParameters.suggestedLatency = Pa_GetDeviceInfo( outputParameters.device )->defaultLowOutputLatency;
        outputParameters.hostApiSpecificStreamInfo = NULL;

        err = Pa_OpenStream(
                  &stream,
                  NULL, /* no input */
                  &outputParameters,
                  SAMPLE_RATE,
                  FRAMES_PER_BUFFER,
                  paClipOff,      /* we won't output out of range samples so don't bother clipping them */
                  patestCallback,
                  &data );
        if( err != paNoError ) goto error;

        sprintf( data.message, "No Message" );
        err = Pa_SetStreamFinishedCallback( stream, &StreamFinished );
        if( err != paNoError ) goto error;

        err = Pa_StartStream( stream );
        if( err != paNoError ) goto error;

        printf("Play for %d seconds.\n", NUM_SECONDS );
        Pa_Sleep( NUM_SECONDS * 1000 );

        err = Pa_StopStream( stream );
        if( err != paNoError ) goto error;

        err = Pa_CloseStream( stream );
        if( err != paNoError ) goto error;

        Pa_Terminate();
        printf("Test finished.\n");

        return err;
    error:
        Pa_Terminate();
        fprintf( stderr, "An error occured while using the portaudio stream\n" );
        fprintf( stderr, "Error number: %d\n", err );
        fprintf( stderr, "Error message: %s\n", Pa_GetErrorText( err ) );
        return err;
    }

Answer 1

Without the plug:, there will be no automatic resampling.

PortAudio does not allow to set your own device name, so you would have to define you own device in ~/.asoundrc or /etc/asound.conf, like this:

pcm.mydevice = "plug:surround51"

and select that in PortAudio (search for it with Pa_GetDeviceCount/Pa_GetDeviceInfo). Alternatively, make it the default device with:

pcm.!default = "plug:surround51"