CD player playback speeds

[Percustard]

Hi all,

Do all CD players (ie: domestic units, PC and Mac installed units, walkman style CD players) all playback at the same speed.

I suspect there would be some variation as in the variation between cassette deck playback speeds.

But, I also suspect that digital clocking may reduce the amount of variation.

Is this true? Or are all CD players a law unto themselves?

Seeya

Mark

[QuikDraw]

I suspect that all CD players that are sync'd to the same clock would run at EXACTLY the same speed. They are programmed to work at 44,100 samples per second. PERIOD! And that's exactly what they'll do based on what the digital clock defines as one second.

Each clock usually runs on its own oscillator. No two oscillators run at EXACTLY the same speed. That's why you'll get pops and clicks when you connect two digital devices together if you don't sync one to the other. Those pops and clicks you hear are the clock speed errors.

The quality of the oscillator has a lot to do with the quality of the clock. Cheaper devices will have clocks with oscillators that are not as stable as some of the better units. Less stability means more drift, or speed changes.

While the better clocks will have more stable oscillators and therefore drift less, no two clocks will run EXACTLY the same frequency. That, again, is why we need to sync our digital devices.

I guess the short answer would be, no. They don't all run the same speed. But it's not like you can hear the difference! You couldn't measure two CD players with a chomatic tuner and actually see a measurable difference in pitch if that's what you mean. (except maybe the cheapest ones!)

Mike

[Percustard]

Thanks Mike.

What would the difference in duration be on a "4 minute" song, say, between the best CD players and the cheapest?

Milliseconds, Seconds, samples?


Just curious?

[where02190]

There would be no difference between players in your 4 minute song. 16 bit 44.1k files must be read as such, and if it is not, the player will not recognize properly and simply will not play.

[where02190]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by po hambo:

(Note to where02190: you can get varispeed CD players (used by DJs) so your statement is not correct.)<HR></BLOCKQUOTE>

No my statement is correct, in these variapeed players, the digtal audio is processed for pitch and time correction, and has nothing to do with the rotation speed of the player, which must remain constant.

[seandaly]

"1x" for an audio CD player is not a constant speed. The part of the data spiral on the outside edge of the disk "spins" much faster than the part of the data spiral nearest the center... so much for the "data transfer" part. next comes the humpty dumpty of outputting a doublebyte value 44,100 x per second. Lots of tricks are possible to increase reliability of the data stream at these two levels (motor reliability, oversampling...). in my experience Red Book CD audio has no audible variation - I include computer CD-ROM drives which all have basic Red Book firmware and crappy D/A converters onboard. On the other hand I have experienced playback problems with hard-disk PCM audio, but never speed variation problems, just sample rate problems due to a config error where you get chipmunk effect...

- Sean

[where02190]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by po hambo:
Nick

Think about it. You run the music 12% fast for any time at all and you don't allow the CD to go any faster than normal. I'll let you mull it over.
(I like Busta Drule though, a real plus point for your studio).<HR></BLOCKQUOTE>

the lazer is always reading far ahead o what you are actually listening to. If you try to run a 5 minute sond on one of these DJ players a double speed, it iwll eventually choke, as it is not reading that far ahead, and the buffer gets caught up to by the converter.(I think I said that right...) Anyway, my point is that the CD is not being read at the point you are hearing it, rather far ahead actually, and more memory the player has the further ahead it is reading.

BD says woof!!

[ManhtnProjct]

for what it's worth..

Because I am a freak, over the last 7 years I have been listining to mixes that I have done on many diferent systems, from a cheap portable CD walkmans to cheap boom box's to big pro home audio gear and studio pro quality gear, I have found that there are slight variations in tempo on cheaper cd players. I think this has to do with cheap 44.1 clocks. This is a good topic, I would like to know more..

[Percustard]

An hypothetical:

I send a 5 minute guide track of a mix on Redbook CD

They import it to protools and put their tracks on.

They do a mix (minus the guide of course) and send it back as AIFF 24 bit.

I import their tracks into the session that I made the guide from in the first instance.

Given that I can synch up everthing at the start of each track (maybe with a click)

Will it all be in synch (my tracks and my friends tracks) at the end of the 5 minute track.

[Kev]

I did a similar thing with a Yamaha MD 8 track and it all worked just fine.

The guide track was very slightly out at the end of the song .... less that 5 samples and through the song had some very slight differences in waveform. I guess the compression on the YamahaMD8 did different things??

BUT I was amazed at how well it all worked and it did give the musician extra tracks to play on to. Though he had to bring it back to me to hear the whole song.

Remember 'sound on sound' and 'track bounce' ..???