/** @file patest_dither.c	@ingroup test_src	@brief Attempt to hear difference between dithered and non-dithered signal.	This only has an effect if the native format is 16 bit.	@author Phil Burk  http://www.softsynth.com*//* * $Id: patest_dither.c 1097 2006-08-26 08:27:53Z rossb $ * * 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   (5)#define SAMPLE_RATE   (44100)#ifndef M_PI#define M_PI  (3.14159265)#endif#define TABLE_SIZE   (200)typedef struct paTestData{    float sine[TABLE_SIZE];    float amplitude;    int   left_phase;    int   right_phase;}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 sineCallback( const void *inputBuffer, void *outputBuffer,                         unsigned long framesPerBuffer,			             const PaStreamCallbackTimeInfo *timeInfo,			             PaStreamCallbackFlags statusFlags, void *userData ){    paTestData *data = (paTestData*)userData;    float *out = (float*)outputBuffer;    float amplitude = data->amplitude;    unsigned int i;    (void) inputBuffer;        for( i=0; i<framesPerBuffer; i++ )    {        *out++ = amplitude * data->sine[data->left_phase];  /* left */        *out++ = amplitude * data->sine[data->right_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;    }    return 0;}/*****************************************************************************//*    V18 version did not call Pa_Terminate() if Pa_Initialize() failed.    This V19 version ALWAYS calls Pa_Terminate(). PS.*/PaError PlaySine( paTestData *data, PaStreamFlags flags, float amplitude );PaError PlaySine( paTestData *data, PaStreamFlags flags, float amplitude ){    PaStream*           stream;    PaStreamParameters  outputParameters;    PaError             err;    data->left_phase = data->right_phase = 0;    data->amplitude  = amplitude;    err = Pa_Initialize();    if (err != paNoError)        goto done;    outputParameters.device = Pa_GetDefaultOutputDevice();  /* default output device */    outputParameters.channelCount = 2;                      /* stereo output */    outputParameters.hostApiSpecificStreamInfo = NULL;    outputParameters.sampleFormat = paFloat32;      /* 32 bit floating point output. */                                                    /* When you change this, also    */                                                    /* adapt the callback routine!   */     outputParameters.suggestedLatency = Pa_GetDeviceInfo( outputParameters.device )                                        ->defaultLowOutputLatency;   /* Low latency. */    err = Pa_OpenStream( &stream,                         NULL,                              /* No input. */                         &outputParameters,                         SAMPLE_RATE,                         1024,                              /* frames per buffer */                         flags,                         sineCallback,                         (void*)data );    if (err != paNoError)        goto done;    err = Pa_StartStream( stream );    if (err != paNoError)        goto done;    Pa_Sleep( NUM_SECONDS * 1000 );    printf("CPULoad = %8.6f\n", Pa_GetStreamCpuLoad(stream));        err = Pa_CloseStream( stream );done:    Pa_Sleep( 250 );  /* Just a small silence. */    Pa_Terminate();    return err;}/*******************************************************************/int main(void);int main(void){    PaError     err;    paTestData  DATA;    int         i;    float       amplitude = 4.0 / (1<<15);        printf("PortAudio Test: output EXTREMELY QUIET sine wave with and without dithering.\n");    /* initialise sinusoidal wavetable */    for( i=0; i<TABLE_SIZE; i++ )    {        DATA.sine[i] = (float) sin( ((double)i/(double)TABLE_SIZE) * M_PI * 2. );    }    printf("\nNo treatment..\n"); fflush(stdout);    err = PlaySine( &DATA, paClipOff | paDitherOff, amplitude );    if( err < 0 ) goto done;    printf("\nClip..\n");    fflush(stdout);    err = PlaySine( &DATA, paDitherOff, amplitude );    if( err < 0 ) goto done;    printf("\nClip and Dither..\n");    fflush(stdout);    err = PlaySine( &DATA, paNoFlag, amplitude );done:    if (err)        {        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 ) );        err = 1; /* Though PlaySine() already called Pa_Terminate(), */        }        /* we may still call Pa_GetErrorText().             */    else        printf("\n(Don't forget to turn the VOLUME DOWN after listening so carefully.)\n");    return err;  /* 0 or 1. */}