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  #1  
Old 2005-03-11, 05:30 AM
Andy L Andy L is offline
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What does PCM stand for?

I've seen a few lineages like this recently...

SBD > MR > PCM > DAT > CDR

...and I can't work out what PCM stands for. Can anyone help me out?
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  #2  
Old 2005-03-11, 05:38 AM
62v8 62v8 is offline
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Re: What does PCM stand for?

PCM is the shortform of "Pulse Code Modulation".
For the layman ....
Slice a soundwave at your nominated sample rate and you end up with a lone spike that is represented as a voltage. Translate that with whatever number of bits (4/8/16/20/24 etc) you are using for the quantisation process.

This process has been around for a very long time. The fundamental step of any analog to digital conversion.

There is more to it but I'm sure you can find it if you need to.
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  #3  
Old 2005-03-11, 05:38 AM
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rherron rherron is offline
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Re: What does PCM stand for?

PCM, Pulse Code Modulation (developed in 1939), is a standard method for digitizing analog audio signals. This format is an uncompressed, raw bit stream, linear (transmitted in a linear series meaning that the stream of the signal is sequential rather than random and the amplitude of both the of the input signal and output signal remain at a fixed ratio and a sinusoidal wave input signal will result in a sinusoidal wave output signal at the same frequency), signed two's complement, fixed point encoded data file. A PCM encoder (ADC) may sample analog sound from 8,000 times per second (8 KHz) and use 8-bits to represent each sample, is usually utilized at 44.1 KHz and 16-bit resolution to match CD Audio standards, and can encode at 96 KHz and 24-bit (approximate). The procedure uses only two alternating pulse values (1 and 0) duplicating binary code. This codec creates a raw (RAW) data file (no header or footer information describing sample rate, sample resolution, monaural or stereo) and gives us only 256 possible amplitude values (based on 8-bit binary numbering). When the codec is set to sample at the Audio CD level at 44.1 KHZ sample rate (44,100 samples per second), with 16-bit resolution per sample (65,536 possible amplitude levels), this results in a file that requires 1,411 Kbps (kilobits per second, or 1.4MB) bit rate for representation / playback of one second of stereo music.

Ever heard of Google?

Rob
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  #4  
Old 2005-03-11, 05:48 AM
Andy L Andy L is offline
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Re: What does PCM stand for?

Actually, I had used Google beforehand (why the saracasm?), but I didn't realise PCM referred to the process of A/D conversion. I thought it was some kind of physical medium, like everything else in that lineage.
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  #5  
Old 2005-03-11, 05:58 AM
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rherron rherron is offline
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Re: What does PCM stand for?

Saracasm retracted. Was just joking. Sorry.

Rob
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  #6  
Old 2005-03-11, 06:35 AM
wazoo2u wazoo2u is offline
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Re: What does PCM stand for?

Quote:
Originally Posted by Andy L
Actually, I had used Google beforehand (why the saracasm?), but I didn't realise PCM referred to the process of A/D conversion. I thought it was some kind of physical medium, like everything else in that lineage.
In this case, it's D/A conversion, not A/D.

Lineage doesn't refer exclusively to physical mediums but rather refers to both the processing and storage that is used to process and preserve the signal.

In your given lineage, "SBD > MR > PCM > DAT > CDR" one would assume that the "MR" is some sort of digital storage medium (PCM data on analog tape), since the PCM decoding stage > DAT would not be necessary if the Master Reel was analog (DAT having onboard A>D converters). Since the storage medium is PCM digital, it doesn't matter much what kind of physical medium (video tape or multitrack) was used, but it might be nice to specify the decoder used. You will also often see lineage that include the model sound card and also the DAW's used to process the signal.

And also.... rherron was being POLITELY sarcastic in answering your question. WHY ???? BECAUSE...... while many people who hang in tech forums are more than happy to undertake the challenge of solving problems and exercising their brains to benefit others, it is always preferred that the questioner has made the MINIMUM effort to look into the issue on their own, rather than oblige the forum member to answer the same question over and over, or (as in this case) conduct a mini lesson in audio engineering. A lot of times, you'll LEARN a lot about a subject from just the peripheral discussion about a topic, but it always will buy you a dose of respect if you take the time to TRY to work out the problem or question first. One of the basic techniques that I use with my experienced computer friends for problem solving basically consists of discussing exactly where to LOOK for information about the problem. You'll always learn more when you start skimming and absorbing material this way.
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  #7  
Old 2005-03-11, 07:12 AM
Andy L Andy L is offline
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Re: What does PCM stand for?

Quote:
Originally Posted by wazoo2u
And also.... rherron was being POLITELY sarcastic in answering your question. WHY ???? BECAUSE...... while many people who hang in tech forums are more than happy to undertake the challenge of solving problems and exercising their brains to benefit others, it is always preferred that the questioner has made the MINIMUM effort to look into the issue on their own, rather than oblige the forum member to answer the same question over and over, or (as in this case) conduct a mini lesson in audio engineering. A lot of times, you'll LEARN a lot about a subject from just the peripheral discussion about a topic, but it always will buy you a dose of respect if you take the time to TRY to work out the problem or question first. One of the basic techniques that I use with my experienced computer friends for problem solving basically consists of discussing exactly where to LOOK for information about the problem. You'll always learn more when you start skimming and absorbing material this way.
I agree that it can be annoying to a regular when people ask before searching. But I resent the accusation that I made no effort at all to look into the issue myself - I always search before I ask a question on any forum. For example, I've learned about FLAC fingerprints and shntool from the FAQ here, but this PCM question has had me stumped for a while. Before I started this topic, I searched the alt.music.bootlegs FAQ with no luck.

If I had posted on this site every time I had a tech question, my post count would be twice what it is. Have a look through Technobabble and see how many threads I've started in the past. Not many, huh? This is the first tech question I've asked here and I get flamed for it - I guess I'll know not to ask in the future. This is a good site, but IMO, there's a group of people here (mentioning no names) with an attitude problem who are all too willing to jump on people at any opportunity.
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  #8  
Old 2005-03-11, 08:11 AM
4candles 4candles is offline
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Re: What does PCM stand for?

Quote:
Originally Posted by Andy L
I've seen a few lineages like this recently...

SBD > MR > PCM > DAT > CDR

...and I can't work out what PCM stands for. Can anyone help me out?
MR will be Master Reels

Sony make a range of DAT recorders with the "PCM" model prefix (e.g. Sony PCM-M1). It could possibly refer to that - i.e. the DAT recorder that is between the Master Reel and the actual DAT tape in the lineage.
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  #9  
Old 2005-03-11, 09:53 AM
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ssamadhi97 ssamadhi97 is offline
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Re: What does PCM stand for?

as far as I can tell/guess in this case PCM is actually referring to Sony PCM-1610/1630 digital audio systems which used 3/4" U-Matic cassettes as recording medium. Apparently old but pro-grade stuff.

Guess someone who has more knowledge on the history of audio recording devices and methods can shed some light here.

some references:
http://www.masterdigital.com/24bit/c...ngformats.html
http://umatic.palsite.com/format.html
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  #10  
Old 2005-03-11, 10:01 AM
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ssamadhi97 ssamadhi97 is offline
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Re: What does PCM stand for?

oh yes, while doing research on the topic (it's the result of 5-10 minutes of googlin' btw ) I bumped into this rather interesting post on mastering procedures:

http://www.planetz.com/forums/viewto...03&forum=21&10

have fun, (re)mastering geeks
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  #11  
Old 2005-03-11, 04:20 PM
uhclem
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Re: What does PCM stand for?

Quote:
Originally Posted by rherron
... this results in a file that requires 1,411 Kbps (kilobits per second, or 1.4MB) bit rate for representation / playback of one second of stereo music.
1,411 Kb/s = 176.375 KB/s not 1.4 MB/s.
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  #12  
Old 2005-03-11, 07:18 PM
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jraras jraras is offline
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Re: What does PCM stand for?

Here's a slightly more qualitative and historical definition/background, plus the best resource around for issues of these sorts.

PCM is, as others here have mentioned, "pulse code modulation". This "technology" is still used today. However, as it pertains this lineage it is telling you that the MR (master reel) was transferred to a digital medium using PCM before DAT was around. So, despite the fact that both DAT and PCM use PCM technology the use of it in this lineage is to differentiate the two. The main difference is the actual tapes that were used and that 44.1kHz was NOT the sampling rate used, it is actually something just slightly less--which, will actually clock and lock (most of the time) digitally if you go PCM > DAT, but many people go analog out of the PCM deck to transfer to DAT, due to the inherent imperfect nature of the D>D transfer (the decimal difference in sampling rates).

PCM is seen a lot in Grateful Dead audio sources, as lots of the master reels were transferred to PCM and in the 80's (pre-DAT) many of the main GD tapers (Sean from LA for instance) were running Schoeps and other HQ condenser mics/pre-amps into PCM decks (which were BIG, btw) to master shows.

Here is the digital-audio bible:

http://www.solorb.com/dat-heads/FAQ

Enjoy!!

JR

Quote:
Originally Posted by Andy L
I've seen a few lineages like this recently...

SBD > MR > PCM > DAT > CDR

...and I can't work out what PCM stands for. Can anyone help me out?
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  #13  
Old 2005-03-11, 08:29 PM
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jameskg jameskg is offline
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Re: What does PCM stand for?

Glad someone finally posted it, after so many completely sarcastic and ignorant answers. It was a viable question, as PCM could mean several things. In my experience (which is limited), I've found that seeing PCM in a lineage usually refers to the Sony unit being used at that point, often using a betamax or regular VHS unit to record the information digitally.

Good question.
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