Re: Data Types for Extracting samples from Audio Buffer

Joseph Ayers Mon, 06 Oct 2008 04:27:46 -0700

I got the code for extracting samples from an Audio Buffer to compileand run without errors as:

        unsigned short *ippointer =  (unsigned short *)abl->mBuffers[0].mData;
        unsigned short *idpointer =  (unsigned short *)abl->mBuffers[1].mData;
        ipbuf = [[NSMutableArray alloc] init];
        idbuf = [[NSMutableArray alloc] init];
        NSNumber* ipsamp = [[NSNumber alloc] init];
        NSNumber* idsamp = [[NSNumber alloc] init];
        nsamples = abl->mBuffers[0].mDataByteSize;


        for (isamp = 1; nsamples; isamp++){

ipsamp = [NSNumber numberWithUnsignedShort:(unsignedshort)ippointer[isamp]];

                     [ipbufaddObject:ipsamp];

idsamp = [NSNumber numberWithUnsignedShort:(unsignedshort)idpointer[isamp]];

                     [idbufaddObject:idsamp];
                NSLog(@" isamp %d ipsamp %d idsamp %d",isamp,ipsamp,idsamp);
        }

2008-10-06 07:22:45.768 Roboplasm[29177:813] isamp 108534 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.768 Roboplasm[29177:813] isamp 108535 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.768 Roboplasm[29177:813] isamp 108536 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.769 Roboplasm[29177:813] isamp 108537 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.769 Roboplasm[29177:813] isamp 108538 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.769 Roboplasm[29177:813] isamp 108539 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.770 Roboplasm[29177:813] isamp 108540 ipsamp4255904 idsamp 4255904

Program received signal:  “EXC_BAD_ACCESS”.

2008-10-06 07:22:45.770 Roboplasm[29177:813] isamp 108541 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.770 Roboplasm[29177:813] isamp 108542 ipsamp4255904 idsamp 42559042008-10-06 07:22:45.771 Roboplasm[29177:813] isamp 108543 ipsamp4255904 idsamp 4255904


on Line:

ipsamp = [NSNumber numberWithUnsignedShort:(unsignedshort)ippointer[isamp]];

nsamples is 213120 so the loop bombed before reaching the end of thebuffers

I'm suspicious that values like 4255904 are inappropriate for 16 bitaudio samples.


How can I determine what is going wrong here.

Thanks,
Joseph



On Oct 5, 2008, at 2:32 PM, Jacob Lukas wrote:

On Oct 5, 2008, at 09:47, Joseph Ayers wrote:

I'm trying to extract the audio samples from an audio bufferreturned from the QuickTime Audio extraction API into aNSMutableArray of NSNumbers.
<snip>

The code I am using is:

        AudioBufferList* abl;   
     NSMutableArray * ipbuf;
        NSMutableArray * idbuf;
        NSNumber* ipsamp;
     NSNumber* idsamp;
unsigned short *ippointer = (unsigned short *)abl->mBuffers[0].mData;unsigned short *idpointer = (unsigned short *)abl->mBuffers[1].mData;
        for (isamp = 1; abl->mBuffers[0].mDataByteSize;isamp++){
                [ipsamp initWithUnsignedShort:(unsigned short)ippointer[isamp]];
                     [ipbuf insertObject:ipsamp atIndex:isamp];
                [idsamp initWithUnsignedShort:(unsigned short)idpointer[isamp]];
                     [idbuf insertObject:idsamp atIndex:isamp];
        }
The program crashes on the line
[ipsamp initWithUnsignedShort:(unsigned short)ippointer[isamp]];with
Program received signal:  “EXC_BAD_ACCESS”.


Try this on for size:

// Edited in Mail -- not guaranteed to even compile
// Completely untested
AudioBufferList* abl = /* fetch valid AudioBufferList */;       
NSMutableArray * ipbuf = [NSMutableArray array];
NSMutableArray * idbuf = [NSMutableArray array];
NSNumber* ipsamp = nil; // not strictly necessary
NSNumber* idsamp = nil;
unsigned short *ippointer =  (unsigned short *)abl->mBuffers[0].mData;
unsigned short *idpointer =  (unsigned short *)abl->mBuffers[1].mData;

// Skipping first sample
// where is isamp declared?
for (isamp = 1; isamp < abl->mBuffers[0].mDataByteSize; isamp++){

ipsamp = [NSNumber numberWithUnsignedShort:(unsignedshort)ippointer[isamp]];

        [ipbuf addObject:ipsamp];

idsamp = [NSNumber numberWithUnsignedShort:(unsignedshort)idpointer[isamp]];

        [idbuf addObject:idsamp];
}

-Jacob


Joseph Ayers, Professor
Department of Biology and
Marine Science Center
Northeastern University
East Point, Nahant, MA 01908
Phone (781) 581-7370 x309(office), x335(lab)
Boston: 444 Richards Hall (617) 373-4044
Cellular (617) 755-7523, FAX: (781) 581-6076
eMail: [EMAIL PROTECTED]
http://www.neurotechnology.neu.edu/






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