ios core audio: modifying aurioTouch to save pcm data

As an exercise, I'm trying to modify aurioTouch so that it saves the first 60 seconds of PCM that come in through the mic. I'm avoiding higher-level libs because I want to build some low-latency real-time processing on top of this. I did this by simply creating a big saveBuffer, and then simply appending the data_ptr[2] value stored in drawBuffers[] for each of the "inNumberFrames" per call to PerformThru...then, after 60 seconds has elapsed, I dump the buffer to disk in one shot.

I tried this code by feeding in a uniform click. The problem is that when开发者_如何学JAVA I visualize this saveBuffer data in gnuplot, I get peaks at non-uniform times, off by 30-40% from the steady click, meaning some peaks are close together while others are far apart. I can see the input click .wav and that it is very even, but the saveBuffer plot has bizarre peaks. It makes me wonder if I am saving the pcm data correctly? Perhaps I'm somehow taking too long and losing data as a result?

The changes in PerformThru() I have:

{ // allocate buffer static int *saveBuffer = ( int * ) malloc( 10000000 * sizeof( int ) ); . . .

    SInt8 *data_ptr = (SInt8 *)(ioData->mBuffers[0].mData);

    for (i=0; i<inNumberFrames; i++)
    {
        if ((i+drawBufferIdx) >= drawBufferLen)
        {
            cycleOscilloscopeLines();
            drawBufferIdx = -i;
        }
        drawBuffers[0][i + drawBufferIdx] = data_ptr[2];

        // XXXX I added this line
        if ( saveBuffer ) { saveBuffer[ saveBufferIdx++ ] = ( data_ptr[ 2 ] ); }


        data_ptr += 4;
    }

    // XXX - I added this block:  dump saveBuffer after 60 seconds
    if ( saveBuffer && ( CAHostTimeBase::HostDeltaToNanos( initialHostTime, inTimeStamp->mHostTime ) / 1000000000 ) > 60 )
    {
        std::ofstream bufferOut;
        bufferOut.open( "pcmBuffer.txt" );
        for ( UInt64 i = 0; i < saveBufferIdx; i++ )
        {
            bufferOut << saveBuffer[ i ] << std::endl;
        }
        bufferOut.close();
        free( saveBuffer );
        saveBuffer = 0;
    }
    drawBufferIdx += inNumberFrames;
}

---

Use CAMediaCurrentTime ( media current / current media -- I always forget which way round )

Gosh this source code is butt ugly, whoever wrote it at Apple has a lot to learn in terms of writing readable code. The fact that it is actually used as a public sample is just a joke.

it looks like you are doing everything right. Why don't you try disabling everything else and ONLY feeding the samples into your buffer?

I have done this when I was writing a pitch detector and it worked fine. once I had 30 seconds of samples I just printed everything onto the console much as you are saving to file.

I really think there is much more benefit in coding a visualiser from scratch. AurioTouch is a mess, and it will take longer to figure out how it works then it would take to actually build one.