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#88625 - 04/11/05 08:08 PM Re: Dumb question about cd players
pmbuko Offline
shareholder in the making

Registered: 04/02/03
Posts: 16273
Loc: Leesburg, Virginia
Haoleb,

One can also assume that many people who say you CAN hear a difference (in CD players connected digitally) don't really have any idea about what goes on inside the player, either.

CD drive and pickup mechanisms have matured significantly since they were invented and are able to easily track the pits and nulls along the spiral tracks written on the disc. Sony Discmans have been able to do this task for years.
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#88626 - 04/11/05 10:42 PM Re: Dumb question about cd players
nautec Offline
old hand

Registered: 03/27/05
Posts: 64
Loc: Tucson, AZ
Just my 0.02 cents. My $29 Norcent DVD player generates a lot of heat and is noisy. My $129 Sony Dvd Player is slimming and clearer. I see a differnece in picture quality. If you compare a $350 dvd player to my $29 Norcent, yeah it makes a difference.

And that ends a paragraph of nonsense clearly written by someone who is drunk.

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#88627 - 04/11/05 10:47 PM Re: Dumb question about cd players
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17766
Loc: NoVA
That's also visual, where the industry is arguably not as mature, and the device is doing digital to analog conversion.

If you're just pulling digital bits off the CD and throwing them out a digital connection [the way most (?)] people have their CD players set up, there is no reason in this day and age that there should be an audible difference. It's not magic, people.
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#88628 - 04/12/05 01:18 AM Re: Dumb question about cd players
BrenR Offline
connoisseur

Registered: 12/10/03
Posts: 3602
Loc: Winnipeg MB Canada
Pits. Lasers. Laser reads pits in media. Same as your $29 CD-ROM... 8-bit bytes, two together make a 16 bit word. Put two words together, you get one stereo sample. Repeat 44,100 times a second. Lather, rinse, repeat.

If you're taking out an analog signal, things get a bit different based on how good the resistor matching is... unless you have a 1-bit DAC (or delta-sigma modulator)... waitaminute... why is 1 bit better than 16 bit?

A 1-bit DAC oversamples each bit (just 0 or 1) in the byte a repeated number of times (think of it as having a few proofreaders) and either averages them or throws out stray values, whatever method the manufacturer uses for error correction... if it reads it 100 times and sees a 0 ninety-nine times and a 1 once - it calls it a 0.

An 8-bit DAC (use any bit depth here just change the math!) reads in a full-range value (in this case, 0-255) and uses resistors (other methods are available, of course - Ladder DACs, etc) to set a threshold (more than half = 0, less than half = 1) for each bit.
**edit** That should of course be... less than half = 0, more than half =1 **/edit**

Maybe the opposite is easier to understand - this is how an 8-bit ADC (analog to digital converter) works. Imagine the values 0-255 expressed in voltage between 0-1 volts. Imagine the "read" voltage is .643V :
128) first pass for the MSB (most significant bit) - it's above 0.5 v (half - our threshold) so set the bit as 1 (1xxxxxxx) and take the value of the bit (0.5) away from the number (leaving 0.143)
64) multiply by two (to get the next less significant base two value)... 0.286 is it more than half? No, set 0 (10xxxxxx), do not take away from the value.
32) multiply by two again - 0.572 - more than half? Yes. Set 1, take away the value of the bit. (101xxxxx) Value is now 0.072
16) 0.072 x 2 = 0.144. More than half? No. Make it 0. (1010xxxx)
8) 0.144 x 2 = 0.288. More than half? No. Make it 0. (10100xxx)
4) 0.288 x 2 = 0.576. More than half? Yes. Make it 1. (101001xx). Take away 0.5 (0.076 is new value)
2) 0.076 x 2 = 0.152. More than half? No. Make it 0. (1010010x)
1) 0.152 x 2 = 0.304. More than half? No. Make it 0. (10100100)

So that equates to a binary representation of the Base10 number 164. Now how close did we get? Divide by 255 (the range) and we get 0.6482 - only .005 volts off of the original value. Pretty darned good for 8 bits. Your CD player is 16 bits (which makes it 256 times "finer" in resolution)... gets you to within a few dozen nanovolts. Now I'm no cable Nazi, but I think even differences in relative humidity are going to make a bigger difference than even 50 nanovolts in a signal.

Bren R.


Edited by BrenR (04/12/05 01:48 AM)

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#88629 - 04/12/05 03:09 AM Re: Dumb question about cd players
tomtuttle Offline
axiomite

Registered: 06/20/03
Posts: 8283
Loc: Tacoma
Definitely 246 toothpicks, yeah. Definitely. 246.
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#88630 - 04/12/05 03:43 AM Re: Dumb question about cd players
nitram Offline
buff

Registered: 04/09/03
Posts: 57
Loc: Santa Rosa, California
re: cable noise

It's actually pretty darn easy to make 50nV noise in unshielded wires (just bend them, or let them vibrate, or wave your hand in front of them, and the capacitance of the wires will pick up the moving charge and generate a current in the 10nA range easy) but the real question is how much noise will be in an audible frequency range. Answer is: basically none, other than 60Hz pickup in some unfortunate systems. So as far as your ears are concerned, clean digital audio frequency signals are pretty easy to generate, digitize, undigitize, transmit with no noise added.

What I don't know is whether audio engineers add imperfections to the raw digital stream to make it sound better. In digital graphics, there's something called "antialiasing", where you try to compensate for imperfect sampling by some kind of interpolation or smoothing. I assume that you can accomplish this in audio by taking the 44kHz signal and doing a low-pass filter on it, say a nice smooth attenuation of all signal above 20kHz.

So maybe a $30 CD player has perfect fidelity but poor antialiasing.

I'd like someone who knows to chime in here, but I bet that a lot of the difference between speakers is in the way they filter out the very high frequency sounds, and that the supposed harshness of Axioms is because they reproduce any harsh, unfiltered digital signal from that $30 CD player with excellent fidelity (garbage in, garbage out), and the supposed warmth of high-end speakers and players and tube amps is because they filter out, in a manner pleasing to most ears, such higher frequency junk.



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#88631 - 04/12/05 03:54 AM Re: Dumb question about cd players
BrenR Offline
connoisseur

Registered: 12/10/03
Posts: 3602
Loc: Winnipeg MB Canada
Strangely, after my super-post up there, I didn't understand a darned thing you said.

Are you talking about oversampling on a player? Or that engineers mix in a special way to compensate for frequencies over the Nyquist limit of 22.05KHz?

Bren R.

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#88632 - 04/12/05 04:57 AM Re: Dumb question about cd players
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10383
Martin, I'm not really certain about those $30 players(suspect they're okay)but the typical $100 players all have 8X oversampling(and have had for years)which allows relatively gentle filtering to remove the response beginning above 20KHz and reducing it to below audibility by 22.05KHz, so there's no harshness as a format. Of course individual recordings can be lousy, but that has nothing to do with the digital process itself.
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#88633 - 04/13/05 03:48 AM Re: Dumb question about cd players
nitram Offline
buff

Registered: 04/09/03
Posts: 57
Loc: Santa Rosa, California
Yeah I think you're right, JohnK, check out
http://www.audioholics.com/techtips/specsformats/upsamplingvsoversampling1.php
It has a nice description of oversampling using electrical engineering lingo.

If oversampling isn't built in on the standard commodity DAC then the $30 players don't have it (an addition $0.10 part on a player that costs a couple bucks to manufacture won't make the cut). Judging from the NRC anechoic chamber measurements that Ian's been publishing for various Axioms, there's a dip in the high teen kHz in the tweeter frequency response, but there's still response at 20kHz, so if there is >22.05kHz digital crap it'll be played by the Axioms. Maybe some receivers have the ability to filter this stuff out too.
--Martin

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#88634 - 04/13/05 04:55 AM Re: Dumb question about cd players
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10383
Martin, although I haven't studied the very least expensive players, they all have to have a DAC for analog output. All DACs, even the ones available to manufacturers for less than $1 each in quantity, have used oversampling for quite a few years. So, I'd doubt that even those $30 players are getting any imaging distortion from over 22.05KHz.
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