Re: How to play RAW PCM data using CoreAudio?
Re: How to play RAW PCM data using CoreAudio?
- Subject: Re: How to play RAW PCM data using CoreAudio?
- From: Brian Willoughby <email@hidden>
- Date: Thu, 23 Apr 2009 14:22:27 -0700
If your generation code runs fast enough, then you do not need the
interim step of saving it in a file. You could use any of the
CoreAudio features which use a callback (whether direct audio ouput,
or AudioUnit Music Instrument), and simply calculate the data on the
fly, providing the samples requested. This would change your
makeChirp() slightly, because, rather than loop through all samples,
you would only produce the exact number of sample requested in the
current callback. Also, you would need to provide subsequent pieces
of the waveform for each callback until the chirp is completed - and
then you would provide silence to the callback until you want to
product another chirp.
Look through the CoreAudio Examples like SinSynth or other callback-
based samples for hints.
However, if that proves too difficult, you could change from saving
the raw NSData to using the CoreAudio AudioFile API to save a CAF
file instead of the raw data. You will certainly be able to open an
audio file created with the AudioFIle API (Or ExtAudioFile, if needed).
Brian Willoughby
Sound Consulting
On Apr 23, 2009, at 08:13, malcom wrote:
Hi, I've finally made my own chirp signal and I've written it into a
file (the code is below).
At this time I need to get it played by Core Audio. I've successfully
imported it in Audacity and it works perfectly
(44,100/16bit/mono/endianess)..
I've tried with this code but it does works because seems that CA
can't open raw PCM data file (and inside the list of formats there is
not mention to raw pcm data format).
Anyone can suggest me a way to play it?
void makeChirp(double freq_start,double freq_end,int
duration_secs,long sample_rate, int bits_persample) {
long len_array = (long)duration_secs*sample_rate; // this is the
number of samples to generate
short wavesamples[len_array]; // this is our array of samples
int i; for (i=0; i < len_array; i++) // some funky initializations...
wavesamples[i] = 0;
double k = (freq_end-freq_start)/len_array;
double freq = freq_start; // this is our time-to-time frequency value
double omega = (double)(PI / sample_rate);
long t;
for (t=0; t < len_array; t++) {
freq += k; // increase frequency over the time with the omega value
double c_sample = sin(omega*freq*t)*MAX_INT;
wavesamples[t] = (short)c_sample;
}
NSData *d = [[NSData alloc] initWithBytes: wavesamples
length:len_array];
[d writeToFile: @"/Users/malcom/Desktop/file.pcm" atomically:YES];
}
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