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From: Jerry Avins on 15 Nov 2009 17:18 Richard Dobson wrote: > Jerry Avins wrote: >> Richard Dobson wrote: >> >>> It is a ~lot~ less work, and a whole lot safer, just to use an >>> established library to do the job. >> >> Yes. I stand corrected and abashed, but the OP still needs to know >> what a .wav file is -- in particular, _his_ .wav file. He can use >> libsndfile to read the header. (Do you think he knows about headers?) >> >> Jerry > > > The only essential point to make in answering that question is that a > WAVE (or AIFF) file does not have a fixed-length header. The OP shoudl > disregard any suggestion to the contrary. You can't take a short cut and > say 'the audio starts at byte 34' or whatever. Well, you could, just, in > writing a file, but not in reading one. There are unfortunately many > examples (including many self-styled "documentation" pages) on the net > where that assumption is made, implicitly or explicitly (the original > matlab implementation of "wavread" suffered just this problem, among > other things). I long ago lost count of the number of unix programs > especially that broke simply because I gave them a WAVE file with a > longer header than the theoretical minimum. > > All other things being equal, there are only two primary types of > programmer who should really commit the time and effort to delve into > the minutiae of such file formats - writers of soundfile handling > libraries such as Eric with libsndfile (which as I am sure he will > confirm has taken years of work to reach its present extremely > efficient, accurate and comprehensive state), and people who design file > formats (and thus need a custom soundfile library they can freely > "hack"); which is what I have done from time to time (e.g. for phase > vocoder analysis files, and for Ambisonic B-Format). All true. When I write that aaronde needs to know what a .wav file is, I don'r mean the details you enumerate. I mean its format, including header (which I suspect is a surprise to him) and a series of integers whose size and format the header describes. I hope he's still reading. There's a lot he needs to learn from you and Erik. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: glen herrmannsfeldt on 15 Nov 2009 18:30 Jerry Avins <jya(a)ieee.org> wrote: (snip) > Yes. I stand corrected and abashed, but the OP still needs to know what > a .wav file is -- in particular, _his_ .wav file. He can use libsndfile > to read the header. (Do you think he knows about headers?) Some time ago I wrote a program to read WAV files, including extracting the data from the header. It seems, though, that what most do is just skip the appropriate number of bytes. (Programs like cdrecord.) I have one that computes, among others, the peak and RMS values. I thought about posting it but never did. -- glen
From: Randy Yates on 15 Nov 2009 18:44 Erik de Castro Lopo <erikd(a)mega-nerd.com> writes: > [...] Erik, Didn't libsndfile just recently win some type of award or recognition? In any case, thanks for a very useful library. I use it in my spectral analysis tool. -- Randy Yates % "Bird, on the wing, Digital Signal Labs % goes floating by mailto://yates(a)ieee.org % but there's a teardrop in his eye..." http://www.digitalsignallabs.com % 'One Summer Dream', *Face The Music*, ELO
From: aaronde on 15 Nov 2009 18:54 >Richard Dobson wrote: >> Jerry Avins wrote: >>> Richard Dobson wrote: >>> >>>> It is a ~lot~ less work, and a whole lot safer, just to use an >>>> established library to do the job. >>> >>> Yes. I stand corrected and abashed, but the OP still needs to know >>> what a .wav file is -- in particular, _his_ .wav file. He can use >>> libsndfile to read the header. (Do you think he knows about headers?) >>> >>> Jerry >> >> >> The only essential point to make in answering that question is that a >> WAVE (or AIFF) file does not have a fixed-length header. The OP shoudl >> disregard any suggestion to the contrary. You can't take a short cut and >> say 'the audio starts at byte 34' or whatever. Well, you could, just, in >> writing a file, but not in reading one. There are unfortunately many >> examples (including many self-styled "documentation" pages) on the net >> where that assumption is made, implicitly or explicitly (the original >> matlab implementation of "wavread" suffered just this problem, among >> other things). I long ago lost count of the number of unix programs >> especially that broke simply because I gave them a WAVE file with a >> longer header than the theoretical minimum. >> >> All other things being equal, there are only two primary types of >> programmer who should really commit the time and effort to delve into >> the minutiae of such file formats - writers of soundfile handling >> libraries such as Eric with libsndfile (which as I am sure he will >> confirm has taken years of work to reach its present extremely >> efficient, accurate and comprehensive state), and people who design file >> formats (and thus need a custom soundfile library they can freely >> "hack"); which is what I have done from time to time (e.g. for phase >> vocoder analysis files, and for Ambisonic B-Format). > >All true. When I write that aaronde needs to know what a .wav file is, I >don'r mean the details you enumerate. I mean its format, including >header (which I suspect is a surprise to him) and a series of integers >whose size and format the header describes. I hope he's still reading. >There's a lot he needs to learn from you and Erik. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� > Yeah still reading.... thanks for the info guys really helped
From: Erik de Castro Lopo on 15 Nov 2009 21:59
Randy Yates wrote: > Didn't libsndfile just recently win some type of award or recognition? If it did, nobody told me :-). Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/ |