Bazirker Posted January 21, 2003 Report Share Posted January 21, 2003 Is PCM the same thing as SPDIF? Do optical, PCM, and SPDIF use the same data and just have a different transfer medium? Quote Link to comment Share on other sites More sharing options...
LostChordSearcher Posted January 22, 2003 Report Share Posted January 22, 2003 Optical uses S/PDIF (Sony/Philips Digital Interface Format), and AFAIK (about 98% sure), it's just PCM with some extra stuff (like SCMS information). Quote Link to comment Share on other sites More sharing options...
Bazirker Posted January 23, 2003 Author Report Share Posted January 23, 2003 OK, so S/PDIF is a format while PCM and optical are transfer methods...right? btw, thanks for the response. Quote Link to comment Share on other sites More sharing options...
highlandsun Posted January 23, 2003 Report Share Posted January 23, 2003 PCM stands for Pulse-Code Modulation. It is an encoding method, not a transfer method. An optical cable that conforms to S/PDIF spec will carry PCM audio as light pulses. A coax cable will do the same with electrical pulses. An uncompressed WAV file stores PCM audio as a sequence of bits. Quote Link to comment Share on other sites More sharing options...
Bazirker Posted January 24, 2003 Author Report Share Posted January 24, 2003 OK, so PCM and S/PDIF are the formats while optical and coaxial are the transfer mediums. Gotcha. (Duh, I forgot all about coaxial being the transfer medium...I bought this radio shack digital converter that converts "PCM" to "optical," and this seemed odd to me as I am used to seeing coaxial to optical.) Thanks for the responses! Quote Link to comment Share on other sites More sharing options...
Andy Posted January 24, 2003 Report Share Posted January 24, 2003 Just a bit of confusion I've found - SPDIF usually means coaxial connection. Occasionally, I have seen an optical connection referred to as SPDIF, but I'm pretty sure this is wrong. Although the actual signal sent is identical (substitute light pulses for electrical pulses), the method of transmission is part of the SPDIF standard. The proper name for optical is TOSLINK. If you've ever seen a graph of a sound wave, then you are most of the way there in terms of understanding what PCM is. The wave is broken down into samples (or points) which make up the wave. Each one of these points has an amplitude and a time. Usually, amplitude is on the up/down axis and time increases as you go from left to right. To make things simple, it is assumed that the time between each sample is constant - this way, only the sampling rate/frequency has to be stored along with the amplitude information. The amplitude is simply the position of the sound wave in the up/down direction. So, a PCM square wave could look like this: -5, -5, -5, 5, 5, 5, -5, -5, -5, 5, 5, 5, -5, -5, -5... Of course, if you open up a .wav file, it won't look very much like this. If you open up a .wav file of a sine wave in notepad then you might see a pattern. Also, there is a bit of header information which says stuff like sampling rate, sample size (the number of different values each sample could have) and for .wav files, it also specifies that the file is PCM encoded since a .wav file can use any type of encoding - including ATRAC3 and MP3. Quote Link to comment Share on other sites More sharing options...
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