BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How to mix PCM wave files with Delphi (not play, only mix)          BorlandTalk.com Forum Index -> Delphi Multimedia View previous topic :: View next topic   Author Message Tom Guest Posted: Sun May 14, 2006 10:14 pm    Post subject: How to mix PCM wave files with Delphi (not play, only mix) Hi. I am making a program with BDS 2006 which should mix several PCM wave files together, manage volume of each wavefile, compress them in MP3, and send them to a broadcast server. I managed to do the read of the file (using mmio functions), to compress the wavedata to mp3 (using acm functions of the api), and to send them to the server (using a socket class i wrote). The problem is i don't know how to mix the PCM wavedata of the files together. In fact, i don't know much about wave principes. I know it's PCM 44100, stereo, 16 bits, but how must i do to mix all data together : an average, an addition ? by word ? I think i managed to adjust volume of the files : i add or remove a percentage of each word of the data for the whole file. Is it the right way ? Best regards, Tom. Back to top Steffen Binas Guest Posted: Mon May 15, 2006 8:14 am    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Tom schrieb: Quote: I think i managed to adjust volume of the files : i add or remove a percentage of each word of the data for the whole file. Is it the right way ? It's simply the average by sample per channel. // Mix one sample of 3 Waves ResultWave := (Wave1 + Wave2 + Wave3) / 3; // Mix one sample with adjusting the volume // Volume is a value (single/double) from 0 to 1 ResultWave := (Wave1 * Volume1 + Wave2 * Volume2 + Wave3 * Volume3) / 3; It's not very fast to use floating point math, but it's easier to write the basic idea down. Regards, Steffen Back to top Tom Guest Posted: Mon May 15, 2006 3:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Thanks for your answer ! Steffen Binas a écrit : Quote: It's simply the average by sample per channel. // Mix one sample of 3 Waves ResultWave := (Wave1 + Wave2 + Wave3) / 3; I saw on a site someone simply adding the 3 values. What will be the result of his method, and yours ? When i work on a 16 bit PCM file (44100 stereo), i suppose i must do the average word by word, is this right ? Regards, Tom Back to top Martin James Guest Posted: Mon May 15, 2006 6:15 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Quote: I saw on a site someone simply adding the 3 values. What will be the result of his method, Overflow and either clipping or worse distortion as the word wraps on coincident peaks. Rgds, Martin Back to top Tom Guest Posted: Mon May 15, 2006 10:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Thank you very much Steffen and Martin, my prog works fine now ! I tried to mix by adding the waves, and by getting the average of the waves, and in fact both methods are interesting. The first (adding) mixes the waves without reducing any level (but with the risk of getting clipping). The second reduces the level of the sounds, but avoids any clipping. This seems very simple, but i didn't know how to do, so thanks a lot for your help. Regards, Tom Back to top Tsviatko Jongov Guest Posted: Tue May 16, 2006 7:14 am    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Hi, Quote: When i work on a 16 bit PCM file (44100 stereo), i suppose i must do the average word by word, is this right ? Yes, because you have 16 bit samples, which is equal to one word. If you have 8 bit PCM you'll have to do the same with each byte. There is also 24 bit and 32 bit PCM (I'm not sure about 64 bit sound, bit it's in pro systems). 44100 Hz means that you have 44100 samples per second, but you'll have to notice that these samples are only for one MONO channel. Since you have stereo 16 bit PCM, you'll have 44100 samples for the left and 44100 for the right channel. In the stream they are mixed like this - LEFT sample, RIGHT sample, LEFT sample, RIGHT sample, .... Example: 44100 Hz, 16 bit, stereo PCM 44100 samples * 2 channels * 16 bit per sample = 176 400 bytes for one second. 48000 Hz, 16 bit, stereo PCM 48000 samples * 2 channels * 16 bit per sample = 192 000 bytes for one second. Hope this will clear up a little the PCM structure. Regards, Tsviatko Jongov johngov at yahoo dot com Back to top Lee_Nover Guest Posted: Tue May 16, 2006 10:14 am    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Quote: Overflow and either clipping or worse distortion as the word wraps on coincident peaks. not if you use a larger value to do the sum the signals are 2bytes, if you add them to a 4 or 8byte value you can avoid clipping with many many channels also beware of signed and unsigned signals - don't mix them Back to top Martin James Guest Posted: Tue May 16, 2006 12:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi not if you use a larger value to do the sum the signals are 2bytes, if you add them to a 4 or 8byte value you can avoid clipping with many many channels also beware of signed and unsigned signals - don't mix them :) I assumed that the output channel was also a 16-bit PCM stream. If the output channel is 48 bits wide, then simple additive mixing would not introduce any clipping/overflow. Rgds, Martin Back to top Lee_Nover Guest Posted: Tue May 16, 2006 1:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Quote: I assumed that the output channel was also a 16-bit PCM stream. If the if it's signed then there's rarely any clipping .. unles all signals have the same phase but you're right that it can still clip in cases like these an AGC could be applied (auto gain control) Back to top Mark Jacobs Guest Posted: Wed May 17, 2006 1:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi "Lee_Nover" <Lee_Nover[nospam]@delphi-si.com> wrote in message news:op.s9m89fttignj8p@stupidirko... Quote: I assumed that the output channel was also a 16-bit PCM stream. If the if it's signed then there's rarely any clipping .. unles all signals have the same phase but you're right that it can still clip in cases like these an AGC could be applied (auto gain control) Or do what Goldwave does, and scan the entire PCM sample for the highest voltage (value) in the channels added together (left channel is 16 bits in each even word, and right in the odd). Then ratio every value in the sample to scale to a reduced maximum that doesn't clip. It gives you a sense of power, playing with sound at this level of engineering! -- Mark Jacobs DK Computing http://www.dkcomputing.co.uk Back to top Thaddy Guest Posted: Fri May 19, 2006 7:14 pm    Post subject: Re: How to mix PCM wave files with Delphi (not play, only mi Mark Jacobs wrote: Even in simple signed integer (1+1) div 2 (mixing) I recommend transferring the whole lot to 32 bit floats first and normalize the lot afterwards. No clipping, pristine audio every time. And the cost is minimal. I have a rather popular and very, very simple freeware BASM library that can help you with it available here: http://members.chello.nl/t.koning8/tdkdsplib.zip I wrote that exactly to do mixing, limiting etc. It is nothing brilliant but it is concise, small, very fast and will do the job better than most. Also note most real good pro software does that. Never use MMX, maybe SSE family or 3DNow and always process in the float domain (be it singles or doubles) You CAN here the difference. 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