alsa - 5.1 带 PortAudio 的 channel

Question

我正在尝试开始使用 PortAudio。我能够毫无问题地构建捆绑的示例文件“paex_sine.c”。这是左声道的正弦波和右声道的不同频率的正弦波。这可以正常工作，没有错误。

我的设置是运行 Puppy Linux Slacko 5.5 的 32 位 PC。它有一个带有 EMU10k1x 芯片的 SoundBlaster SB0200。 Alsa 库是 v1.0.26，驱动程序是 v1.0.24。我已经使用此命令测试了所有 5.1 channel :

% speaker-test -Dplug:surround51 -c6

测试在 6 个 channel 中的每个 channel 上都能正常播放声音，尽管它确实提示管道损坏。这可能是因为在所有 6 个 channel 的测试程序中缓冲区不够大。

我遇到的问题是，当我将“paex_sine.c”修改为在 6 个 channel 而不是 2 个 channel 上运行时，它只会通过右前和左前 channel 播放声音。没有报告错误，2 个 channel 听起来应该如此。我听说在某些情况下 channel 必须取消静音。在 AlsaMixer 和 Puppy 的“Retrovol”(镜像 AlsaMixer)中，我已将 Master、PCM 和 Surround 设置为最大音量，未静音。 PortAudio 中是否有我也必须取消静音的调音台？我可以在正确运行扬声器测试和运行修改后的 paex_sine 示例并仅听到 2 个 channel 之间来回切换。这是我修改过的 paex_sine.c:

    /** @file paex_sine.c        @ingroup examples_src        @brief Play a sine wave for several seconds.        @author Ross Bencina <rossb@audiomulch.com>        @author Phil Burk <philburk@softsynth.com>    */    /*     * $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

如果没有plug:，将不会自动重采样。

PortAudio 不允许设置您自己的设备名称，因此您必须在~/.asoundrc 或/etc/asound.conf 中定义您自己的设备，像这样:

pcm.mydevice = "plug:surround51"

并在 PortAudio 中选择它(使用 Pa_GetDeviceCount/Pa_GetDeviceInfo 搜索)。或者，将其设为默认设备:

pcm.!default = "plug:surround51"