Generare un'onda sinusoidale con le funzioni esterne della libreria PortAudio
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Versione del 14 lug 2014 alle 17:10 di Vuott (Discussione | contributi)
La libreria PortAudio è una libreria per la gestione in tempo reale dei dati audio in entrata ed in uscita. Essa fa parte di un assortimento di API e librerie create per la musica e per altri media.
E' possibile con alcune funzioni esterne della libreria PortAudio generare un'onda sinusoidale. Sarà necessario avere installata nel proprio sistema la libreria condivisa: libportaudio.so.2.0.0
Mostriamo di seguito un possibile codice:
Public Struct PaStreamParameters device As Integer channelCount As Integer sampleFormat As Long suggestedLatency As Float hostApiSpecificStreamInfo As Pointer End Struct Private Const SAMPLE_RATE As Integer = 44100 Private Const FRAMES_PER_BUFFER As Integer = 1024 Private Const FREQUENZA As Short = 440 Private Const paNoError As Integer = 0 Private Const paNoDevice As Integer = -1 Private Const paFloat32 As Integer = 1 Private Const paClipOff As Integer = 1 Library "libportaudio:2.0.0" ' PaError Pa_Initialize(void) ' Library initialization function - call this before using PortAudio. ' This function initializes internal data structures and prepares underlying host APIs for use. Private Extern Pa_Initialize() As Integer ' PaDeviceIndex Pa_GetDefaultOutputDevice( void ) ' Retrieve the index of the default output device. Private Extern Pa_GetDefaultOutputDevice() As Integer ' PaError Pa_OpenStream( PaStream** stream, const PaStreamParameters *inputParameters, const PaStreamParameters *outputParameters, ' double sampleRate, unsigned long framesPerBuffer, PaStreamFlags streamFlags, PaStreamCallback *streamCallback, void *userData ) ' Opens a stream for either input, output or both. Private Extern Pa_OpenStream(PaStr As Pointer, inPa As PaStreamParameters, outPa As PaStreamParameters, sampleRate As Float, fraPBuf As Long, Flags As Long, Callb As Pointer, Data As Pointer) As Integer ' PaError Pa_StartStream( PaStream *stream ) ' Commences audio processing. Private Extern Pa_StartStream(PaStr As Pointer) As Integer ' PaError Pa_WriteStream( PaStream* stream, const void *buffer, unsigned long frames ) ' Write samples to an output stream. Private Extern Pa_WriteStream(PaStr As Pointer, buff As Single[], frames As Long) As Integer ' PaError Pa_CloseStream( PaStream *stream ) ' Closes an audio stream. Private Extern Pa_CloseStream(PaStr As Pointer) As Integer ' PaError Pa_Terminate( void ) ' Library termination function. Private Extern Pa_Terminate() As Integer ' const char *Pa_GetErrorText(PaError errnum) ' Translates the supplied PortAudio error number into a human readable message. Private Extern Pa_GetErrorText(errnum As Integer) As String Public Sub Main() Dim outputParameters As New PaStreamParameters Dim PaStream As Pointer Dim err, fase_sin, fase_des, i, j, k As Integer Dim buffer As New Single[1024, 2] ' Buffer per Uscita stereo Dim sinus As New Single[FREQUENZA] ' Dati dell'onda sinusoidale Dim inc_sin As Integer = 4 Dim inc_des As Integer = 4 For i = 0 To FREQUENZA - 1 sinus[i] = CSingle(Sin((CFloat(i) / CFloat(FREQUENZA)) * Pi * 2.0)) Next err = Pa_Initialize() If err < paNoError Then Error.Raise("Impossibile inizializzare la libreria 'PortAudio': " & Pa_GetErrorText(err)) outputParameters.device = Pa_GetDefaultOutputDevice() ' Dispositivo audio prestabilito If outputParameters.device = paNoDevice Then Error.Raise("Nessun dispositvo audio presente nel sistema !") outputParameters.channelCount = 2 ' Uscita stereo outputParameters.sampleFormat = paFloat32 outputParameters.suggestedLatency = 0.050 outputParameters.hostApiSpecificStreamInfo = Null err = Pa_OpenStream(VarPtr(PaStream), Null, outputParameters, SAMPLE_RATE, FRAMES_PER_BUFFER, paClipOff, 0, 0) If err < paNoError Then Error.Raise("Impossibile aprire un flusso audio: " & Pa_GetErrorText(err)) err = Pa_StartStream(PaStream) If err < paNoError Then Error.Raise("Impossibile avviare il processo audio: " & Pa_GetErrorText(err)) For k = 0 To ((10 * SAMPLE_RATE) / FRAMES_PER_BUFFER) - 1 For j = 0 To FRAMES_PER_BUFFER - 1 buffer[j, 1] = sinus[fase_sin] ' Canale sinistro buffer[j, 0] = sinus[fase_des] ' Canale destro fase_sin += inc_sin If fase_sin >= FREQUENZA Then fase_sin -= FREQUENZA fase_des += inc_des If fase_des >= FREQUENZA Then fase_des -= FREQUENZA Next err = Pa_WriteStream(PaStream, buffer, FRAMES_PER_BUFFER) If err < paNoError Then Error.Raise("Impossibile avviare il processo audio: " & Pa_GetErrorText(err)) Next ' Va in chiusura: err = Pa_CloseStream(PaStream) If err < paNoError Then Error.Raise("Impossibile chiudere il flusso audio: " & Pa_GetErrorText(err)) Pa_Terminate() End
ed una sua leggera variante:
Public Struct PaStreamParameters device As Integer channelCount As Integer sampleFormat As Long suggestedLatency As Float hostApiSpecificStreamInfo As Pointer End Struct Public Struct PaDeviceInfo structVersion As Integer name As Pointer hostApi As Integer maxInputChannels As Integer maxOutputChannels As Integer defaultLowInputLatency As Float defaultLowOutputLatency As Float defaultHighInputLatency As Float defaultHighOutputLatency As Float defaultSampleRate As Float End Struct Private Const SAMPLE_RATE As Integer = 44100 Private Const FRAMES_PER_BUFFER As Integer = 1024 Private Const FREQUENZA As Short = 440 Private Const paNoError As Integer = 0 Private Const paNoDevice As Integer = -1 Private Const paFloat32 As Integer = 1 Private Const paClipOff As Integer = 1 Library "libportaudio:2.0.0" ' PaError Pa_Initialize(void) ' Library initialization function - call this before using PortAudio. ' This function initializes internal data structures and prepares underlying host APIs for use. Private Extern Pa_Initialize() As Integer ' PaDeviceIndex Pa_GetDefaultOutputDevice( void ) ' Retrieve the index of the default output device. Private Extern Pa_GetDefaultOutputDevice() As Integer ' const PaDeviceInfo * Pa_GetDeviceInfo(PaDeviceIndex device) ' Retrieve a pointer to a PaDeviceInfo structure containing information about the specified device. Private Extern Pa_GetDeviceInfo(device As Integer) As PaDeviceInfo ' PaError Pa_OpenStream( PaStream** stream, const PaStreamParameters *inputParameters, const PaStreamParameters *outputParameters, ' double sampleRate, unsigned long framesPerBuffer, PaStreamFlags streamFlags, PaStreamCallback *streamCallback, void *userData ) ' Opens a stream for either input, output or both. Private Extern Pa_OpenStream(PaStr As Pointer, inPa As PaStreamParameters, outPa As PaStreamParameters, sampleRate As Float, fraPBuf As Long, Flags As Long, Callb As Pointer, Data As Pointer) As Integer ' PaError Pa_StartStream( PaStream *stream ) ' Commences audio processing. Private Extern Pa_StartStream(PaStr As Pointer) As Integer ' PaError Pa_WriteStream( PaStream* stream, const void *buffer, unsigned long frames ) ' Write samples to an output stream. Private Extern Pa_WriteStream(PaStr As Pointer, buff As Single[], frames As Long) As Integer ' PaError Pa_CloseStream( PaStream *stream ) ' Closes an audio stream. Private Extern Pa_CloseStream(PaStr As Pointer) As Integer ' PaError Pa_Terminate( void ) ' Library termination function. Private Extern Pa_Terminate() As Integer ' const char *Pa_GetErrorText(PaError errnum) ' Translates the supplied PortAudio error number into a human readable message. Private Extern Pa_GetErrorText(errnum As Integer) As String Public Sub Main() Dim outputParameters As New PaStreamParameters Dim pdi As New PaDeviceInfo Dim PaStream As Pointer Dim err, fase_sin, fase_des, i, j, k As Integer Dim buffer As New Single[FRAMES_PER_BUFFER] Dim sinus As New Single[FREQUENZA] For i = 0 To FREQUENZA - 1 sinus[i] = CSingle(Sin((CFloat(i) / CFloat(FREQUENZA)) * Pi * 2.0)) Next err = Pa_Initialize() If err < paNoError Then Error.Raise("Impossibile inizializzare la libreria 'PortAudio': " & Pa_GetErrorText(err)) outputParameters.device = Pa_GetDefaultOutputDevice() ' Dispositivo audio prestabilito If outputParameters.device = paNoDevice Then Error.Raise("Nessun dispositvo audio presente nel sistema !") outputParameters.channelCount = 2 ' Uscita stereo outputParameters.sampleFormat = paFloat32 pdi = Pa_GetDeviceInfo(outputParameters.device) outputParameters.suggestedLatency = pdi.defaultLowOutputLatency outputParameters.hostApiSpecificStreamInfo = Null err = Pa_OpenStream(VarPtr(PaStream), Null, outputParameters, SAMPLE_RATE, FRAMES_PER_BUFFER, paClipOff, 0, 0) If err < paNoError Then Error.Raise("Impossibile aprire un flusso audio: " & Pa_GetErrorText(err)) err = Pa_StartStream(PaStream) If err < paNoError Then Error.Raise("Impossibile avviare il processo audio: " & Pa_GetErrorText(err)) For k = 0 To ((10 * SAMPLE_RATE) / FRAMES_PER_BUFFER) - 1 For j = 0 To FRAMES_PER_BUFFER - 1 Step 2 buffer[j] = sinus[fase_sin] ' Canale sinistro buffer[j + 1] = sinus[fase_des] ' Canale destro fase_sin += 4 If fase_sin >= FREQUENZA Then fase_sin -= FREQUENZA fase_des += 4 If fase_des >= FREQUENZA Then fase_des -= FREQUENZA Next err = Pa_WriteStream(PaStream, buffer, FRAMES_PER_BUFFER / 2) If err < paNoError Then Error.Raise("Impossibile avviare il processo audio: " & Pa_GetErrorText(err)) Next ' Va in chiusura: err = Pa_CloseStream(PaStream) If err < paNoError Then Error.Raise("Impossibile chiudere il flusso audio: " & Pa_GetErrorText(err)) Pa_Terminate() End