Re: Data Types for Extracting samples from Audio Buffer

Mon, 06 Oct 2008 05:46:01 -0700 

Wow. Many thanks,
That certainly helped. With:

        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)/2;

for (isamp = 0; isamp<nsamples; ++isamp){
ipsamp = [NSNumber numberWithUnsignedShort:(unsigned short)ippointer[isamp]]; 
                     [ipbufaddObject:ipsamp];
idsamp = [NSNumber numberWithUnsignedShort:(unsigned short)idpointer[isamp]]; 
                     [idbufaddObject:idsamp];
        if (isamp < 100) {
                NSLog(@" isamp %d ipsamp %@ idsamp %@",isamp,ipsamp,idsamp);
        }       
}

I get
2008-10-06 08:39:05.177 Roboplasm[32065:813]  isamp 0 ipsamp 0 idsamp 0
2008-10-06 08:39:05.178 Roboplasm[32065:813] isamp 1 ipsamp 15196 idsamp 15214 
2008-10-06 08:39:05.178 Roboplasm[32065:813]  isamp 2 ipsamp 0 idsamp 0
2008-10-06 08:39:05.178 Roboplasm[32065:813] isamp 3 ipsamp 15218 idsamp 15241 
2008-10-06 08:39:05.179 Roboplasm[32065:813]  isamp 4 ipsamp 0 idsamp 0
2008-10-06 08:39:05.179 Roboplasm[32065:813] isamp 5 ipsamp 15250 idsamp 15273 
2008-10-06 08:39:05.179 Roboplasm[32065:813]  isamp 6 ipsamp 0 idsamp 0
2008-10-06 08:39:05.180 Roboplasm[32065:813] isamp 7 ipsamp 15248 idsamp 15327 
2008-10-06 08:39:05.180 Roboplasm[32065:813]  isamp 8 ipsamp 0 idsamp 0
2008-10-06 08:39:05.180 Roboplasm[32065:813] isamp 9 ipsamp 15192 idsamp 15356 
2008-10-06 08:39:05.180 Roboplasm[32065:813]  isamp 10 ipsamp 0 idsamp 0
2008-10-06 08:39:05.181 Roboplasm[32065:813] isamp 11 ipsamp 15128 idsamp 15344 
2008-10-06 08:39:05.181 Roboplasm[32065:813]  isamp 12 ipsamp 0 idsamp 0
2008-10-06 08:39:05.181 Roboplasm[32065:813] isamp 13 ipsamp 15122 idsamp 15341 
2008-10-06 08:39:05.182 Roboplasm[32065:813]  isamp 14 ipsamp 0 idsamp 0
2008-10-06 08:39:05.182 Roboplasm[32065:813] isamp 15 ipsamp 15140 idsamp 15370 2008-10-06 08:39:05.182 Roboplasm[32065:813] isamp 16 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.183 Roboplasm[32065:813] isamp 17 ipsamp 15164 idsamp 15387 
2008-10-06 08:39:05.183 Roboplasm[32065:813]  isamp 18 ipsamp 0 idsamp 0
2008-10-06 08:39:05.183 Roboplasm[32065:813] isamp 19 ipsamp 15214 idsamp 15375 
2008-10-06 08:39:05.185 Roboplasm[32065:813]  isamp 20 ipsamp 0 idsamp 0
2008-10-06 08:39:05.185 Roboplasm[32065:813] isamp 21 ipsamp 15244 idsamp 15334 
2008-10-06 08:39:05.186 Roboplasm[32065:813]  isamp 22 ipsamp 0 idsamp 0
2008-10-06 08:39:05.201 Roboplasm[32065:813] isamp 23 ipsamp 15237 idsamp 15316 
2008-10-06 08:39:05.203 Roboplasm[32065:813]  isamp 24 ipsamp 0 idsamp 0
2008-10-06 08:39:05.210 Roboplasm[32065:813] isamp 25 ipsamp 15180 idsamp 15346 2008-10-06 08:39:05.211 Roboplasm[32065:813] isamp 26 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.211 Roboplasm[32065:813] isamp 27 ipsamp 15128 idsamp 15370 
2008-10-06 08:39:05.212 Roboplasm[32065:813]  isamp 28 ipsamp 0 idsamp 0
2008-10-06 08:39:05.214 Roboplasm[32065:813] isamp 29 ipsamp 15130 idsamp 15382 
2008-10-06 08:39:05.214 Roboplasm[32065:813]  isamp 30 ipsamp 0 idsamp 0
2008-10-06 08:39:05.215 Roboplasm[32065:813] isamp 31 ipsamp 15192 idsamp 15390 2008-10-06 08:39:05.218 Roboplasm[32065:813] isamp 32 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.219 Roboplasm[32065:813] isamp 33 ipsamp 15258 idsamp 15389 2008-10-06 08:39:05.221 Roboplasm[32065:813] isamp 34 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.222 Roboplasm[32065:813] isamp 35 ipsamp 15292 idsamp 15381 
2008-10-06 08:39:05.223 Roboplasm[32065:813]  isamp 36 ipsamp 0 idsamp 0
2008-10-06 08:39:05.224 Roboplasm[32065:813] isamp 37 ipsamp 15304 idsamp 15380 2008-10-06 08:39:05.224 Roboplasm[32065:813] isamp 38 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.228 Roboplasm[32065:813] isamp 39 ipsamp 15300 idsamp 15383 
2008-10-06 08:39:05.229 Roboplasm[32065:813]  isamp 40 ipsamp 0 idsamp 0
2008-10-06 08:39:05.229 Roboplasm[32065:813] isamp 41 ipsamp 15293 idsamp 15375 2008-10-06 08:39:05.230 Roboplasm[32065:813] isamp 42 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.231 Roboplasm[32065:813] isamp 43 ipsamp 15301 idsamp 15361 
2008-10-06 08:39:05.231 Roboplasm[32065:813]  isamp 44 ipsamp 0 idsamp 0
2008-10-06 08:39:05.232 Roboplasm[32065:813] isamp 45 ipsamp 15339 idsamp 15362 2008-10-06 08:39:05.238 Roboplasm[32065:813] isamp 46 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.239 Roboplasm[32065:813] isamp 47 ipsamp 15373 idsamp 15368 2008-10-06 08:39:05.240 Roboplasm[32065:813] isamp 48 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.240 Roboplasm[32065:813] isamp 49 ipsamp 15383 idsamp 15366 2008-10-06 08:39:05.241 Roboplasm[32065:813] isamp 50 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.242 Roboplasm[32065:813] isamp 51 ipsamp 15377 idsamp 15370 2008-10-06 08:39:05.242 Roboplasm[32065:813] isamp 52 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.243 Roboplasm[32065:813] isamp 53 ipsamp 15377 idsamp 15388 2008-10-06 08:39:05.244 Roboplasm[32065:813] isamp 54 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.244 Roboplasm[32065:813] isamp 55 ipsamp 15393 idsamp 15394 2008-10-06 08:39:05.245 Roboplasm[32065:813] isamp 56 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.246 Roboplasm[32065:813] isamp 57 ipsamp 15402 idsamp 15377 2008-10-06 08:39:05.247 Roboplasm[32065:813] isamp 58 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.247 Roboplasm[32065:813] isamp 59 ipsamp 15387 idsamp 15360 2008-10-06 08:39:05.248 Roboplasm[32065:813] isamp 60 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.248 Roboplasm[32065:813] isamp 61 ipsamp 15365 idsamp 15359 2008-10-06 08:39:05.249 Roboplasm[32065:813] isamp 62 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.249 Roboplasm[32065:813] isamp 63 ipsamp 15363 idsamp 15362 2008-10-06 08:39:05.249 Roboplasm[32065:813] isamp 64 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.250 Roboplasm[32065:813] isamp 65 ipsamp 15374 idsamp 15362 2008-10-06 08:39:05.250 Roboplasm[32065:813] isamp 66 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.251 Roboplasm[32065:813] isamp 67 ipsamp 15381 idsamp 15369 2008-10-06 08:39:05.251 Roboplasm[32065:813] isamp 68 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.252 Roboplasm[32065:813] isamp 69 ipsamp 15382 idsamp 15386 2008-10-06 08:39:05.253 Roboplasm[32065:813] isamp 70 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.253 Roboplasm[32065:813] isamp 71 ipsamp 15374 idsamp 15403 
2008-10-06 08:39:05.254 Roboplasm[32065:813]  isamp 72 ipsamp 0 idsamp 0
2008-10-06 08:39:05.254 Roboplasm[32065:813] isamp 73 ipsamp 15360 idsamp 15413 
2008-10-06 08:39:05.255 Roboplasm[32065:813]  isamp 74 ipsamp 0 idsamp 0
2008-10-06 08:39:05.256 Roboplasm[32065:813] isamp 75 ipsamp 15360 idsamp 15410 2008-10-06 08:39:05.256 Roboplasm[32065:813] isamp 76 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.260 Roboplasm[32065:813] isamp 77 ipsamp 15384 idsamp 15394 
2008-10-06 08:39:05.262 Roboplasm[32065:813]  isamp 78 ipsamp 0 idsamp 0
2008-10-06 08:39:05.263 Roboplasm[32065:813] isamp 79 ipsamp 15406 idsamp 15378 2008-10-06 08:39:05.263 Roboplasm[32065:813] isamp 80 ipsamp 0 idsamp 32768 2008-10-06 08:39:05.264 Roboplasm[32065:813] isamp 81 ipsamp 15405 idsamp 15370 
2008-10-06 08:39:05.264 Roboplasm[32065:813]  isamp 82 ipsamp 0 idsamp 0
2008-10-06 08:39:05.265 Roboplasm[32065:813] isamp 83 ipsamp 15405 idsamp 15365 
2008-10-06 08:39:05.266 Roboplasm[32065:813]  isamp 84 ipsamp 0 idsamp 0
2008-10-06 08:39:05.267 Roboplasm[32065:813] isamp 85 ipsamp 15425 idsamp 15349 2008-10-06 08:39:05.269 Roboplasm[32065:813] isamp 86 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.270 Roboplasm[32065:813] isamp 87 ipsamp 15440 idsamp 15339 
2008-10-06 08:39:05.271 Roboplasm[32065:813]  isamp 88 ipsamp 0 idsamp 0
2008-10-06 08:39:05.271 Roboplasm[32065:813] isamp 89 ipsamp 15431 idsamp 15358 2008-10-06 08:39:05.272 Roboplasm[32065:813] isamp 90 ipsamp 32768 idsamp 32768 2008-10-06 08:39:05.272 Roboplasm[32065:813] isamp 91 ipsamp 15415 idsamp 15368 2008-10-06 08:39:05.273 Roboplasm[32065:813] isamp 92 ipsamp 32768 idsamp 0 2008-10-06 08:39:05.274 Roboplasm[32065:813] isamp 93 ipsamp 15413 idsamp 15361 
2008-10-06 08:39:05.274 Roboplasm[32065:813]  isamp 94 ipsamp 0 idsamp 0
2008-10-06 08:39:05.275 Roboplasm[32065:813] isamp 95 ipsamp 15411 idsamp 15337 
2008-10-06 08:39:05.275 Roboplasm[32065:813]  isamp 96 ipsamp 0 idsamp 0
2008-10-06 08:39:05.276 Roboplasm[32065:813] isamp 97 ipsamp 15396 idsamp 15348 
2008-10-06 08:39:05.276 Roboplasm[32065:813]  isamp 98 ipsamp 0 idsamp 0
2008-10-06 08:39:05.277 Roboplasm[32065:813] isamp 99 ipsamp 15385 idsamp 15373 etc...
Note the occurrence of samples with the value of 0 alternating with samples that are reasonable. However, this alternation is not rigid as the 0's can be substituted with reasonable numbers. 

Any idea what's going on here?

Thanks again,
Joseph


On Oct 6, 2008, at 7:53 AM, Graham Cox wrote:



On 6 Oct 2008, at 10:27 pm, Joseph Ayers wrote:
unsigned short *ippointer = (unsigned short *)abl- >mBuffers[0].mData; unsigned short *idpointer = (unsigned short *)abl- >mBuffers[1].mData; 
[]




        nsamples = abl->mBuffers[0].mDataByteSize;

        for (isamp = 1; nsamples; isamp++){
ipsamp = [NSNumber numberWithUnsignedShort:(unsigned short)ippointer[isamp]]; 
                     [ipbufaddObject:ipsamp];
idsamp = [NSNumber numberWithUnsignedShort:(unsigned short)idpointer[isamp]]; 
                     [idbufaddObject:idsamp];



Another problem I just noticed after posting my first reply.
You cast your buffers to unsigned short*. That's OK, presumably each sample is 16 bits. But to me, the field mDataByteSize implies that the buffer size is specified in bytes, not 16-bit words, so the number of samples is this value / 2. 

If your loop were correct, it would look something like:

for( sample = 0; sample < nSamples; ++sample )
{
   sampleValue = ipPointer[sample];
}
Because ipPointer is already declared as a pointer unsigned short, the array subscript will access each sample (2 bytes) at a time, even when incremented by only one. That's a Good Thing™, but makes the proper calculation of the number of *samples* critical. By forgetting to do that, you've overrun the end of your array at about the half-way mark, as you would expect. That's why you're getting the bad access error. 

Graham


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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