Transports

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AudioB

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Transports
« on: 29 Jan 2009, 05:47 pm »
I'm making this threat in regards to CD transports. From what I've read on this site, most people think a cheap transport is just as good as an expensive one. Reasoning being that all it sends is 0s and 1s. For the record, that's what I thought, too.

However, I've stumbled onto this DIY website from a guy who took a long time looking into digital transfer and his conclusions are pretty interesting. With that said, I want to discuss two things:

1) He claims (http://www.lampizator.eu/HERESY/heresy.html) on his myths page (#5) that a digital cable still sends analog signals to the DAC and not 0s and 1s. What do you guys think about this?

2) He claims that a simple mod to a cheap transport will make it a really great transport (http://www.lampizator.eu/LAMPIZATOR/TRANSPORT/CD_transport_DIY.html). He uses a scope to show what the trace of several CD players are and what his modified CD player gets.

There's a lot of science on those pages so I'm looking for someone with a little more understanding than me to chime in.

Tone Depth

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Re: Transports
« Reply #1 on: 29 Jan 2009, 06:22 pm »
I think this might be better if it were moved to Circles\General Discussion as it doesn't pertain solely to AVA.

avahifi

Re: Transports
« Reply #2 on: 29 Jan 2009, 07:27 pm »
I would like to see this moved too, but I won't say where.

Suggestions please as to where to move it.  (Be nice).

Frank Van Alstine

satfrat

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Re: Transports
« Reply #3 on: 29 Jan 2009, 07:44 pm »
Audio Central Circle would be my guess Frank. :D


Cheers,
Robin

oneinthepipe

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Re: Transports
« Reply #4 on: 30 Jan 2009, 12:01 am »
I would still like an AVA transport someday, perhaps based on the CD Pro2 or another high-end mechanism (even if 0s are 0s and 1s are 1s).  I had a very bad experience with a $39.99 Philips DVP, and I still think that the power supply, etc., has a lot to do with a transport's performance within a system.

Anyway, usually after I reply to a thread like this, it immediately ends up in the Intergalactic Wastebin.   :lol:

Zheeeem

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Re: Transports
« Reply #5 on: 30 Jan 2009, 01:46 am »
I would like to see this moved too, but I won't say where.

Suggestions please as to where to move it.  (Be nice).

Frank Van Alstine

Wow.  That links to quite the rant.  Probably general, since the OP seems to have a genuine interest.  But to tell the truth, after reading for about 2 minutes I got a headache.

martyo

Re: Transports
« Reply #6 on: 30 Jan 2009, 01:52 am »
Quote
Anyway, usually after I reply to a thread like this, it immediately ends up in the Intergalactic Wastebin.   

 :icon_arrow: You're banished to sit in front of your SongTowers and crank it.  :lol:   aa

AudioB

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Re: Transports
« Reply #7 on: 30 Jan 2009, 12:55 pm »
Feel free to move this topic if it's not in the right place. I posted it here because I know this topic comes up here and usually there's nothing to back up claims either way.

The question is, does a CD player send 0s and 1s or a square wave to the DAC? The guy from the web site thinks it's a square wave. Now, Mr. Alstine's DAC is supposed to recover all of the square wave if that is what was sent in. But how do we know the digital process sends the full square wave? That's where the second link comes in. The guy tries to show the output of several CD players and that they do not send a perfect square wave. Then he tries a DIY fix.


avahifi

Re: Transports
« Reply #8 on: 30 Jan 2009, 01:10 pm »
You don't need a "perfect' square wave, just good enough so that the circuits can tell what is on and what is off.  Methinks this is a lot of dither over nothing.

Frank

turkey

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Re: Transports
« Reply #9 on: 30 Jan 2009, 02:55 pm »

1) He claims (http://www.lampizator.eu/HERESY/heresy.html) on his myths page (#5) that a digital cable still sends analog signals to the DAC and not 0s and 1s. What do you guys think about this?

That's kind of a red herring. I think he's taking concepts from analog electronics and trying to apply them to digital electronics. You usually wind up with egg on your face when you do that. :)

The key point is whether or not we can recover the transitions that represent 0s and 1s in the analog voltages of the data stream. We can. It's a problem that was solved years ago.

We can even do this at microwave frequencies, so doing it in the low kHz range is not difficult.



AudioB

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Re: Transports
« Reply #10 on: 30 Jan 2009, 03:12 pm »
Hmm...that makes sense. The wave does not need to be a perfect square wave for the DAC to recover all the 0s and 1s the wave represents.

On that note, do we know if CD players get all the bits off a CD? What I mean by that is does the laser read everything on the CD or just most of the data and extrapolates the rest?

Wayner

Re: Transports
« Reply #11 on: 30 Jan 2009, 03:35 pm »
A digital signal is either voltage or no voltage, That is how they get the little 0's and 1's. It's a square wave 'cause it's pulsating DC voltage. In machine design, most digital signals run on +24vdc. When a computer (or PLC) output says "on", is sends 24 volts to the device it wants to be on. When it wants the device to shut off, it opens the relay contacts and that removes the voltage. While this example is not exactly like the digital data stream, it is (in principal) the same techniques.

W

turkey

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Re: Transports
« Reply #12 on: 30 Jan 2009, 04:04 pm »

On that note, do we know if CD players get all the bits off a CD? What I mean by that is does the laser read everything on the CD or just most of the data and extrapolates the rest?

Error correction gives you the actual original data, it doesn't extrapolate anything. It's only in cases where error correction fails that the output diverges from the original.

You'll know when that happens. You then hear various artifacts, depending upon the problem and the design of the hardware. It could be muting, pops or clicks, skipping, etc. But things have to be pretty broken before these sorts of artifacts show up.

With a normal CD player (or transport and DAC, etc.) and CDs in decent condition, error correction fully corrects any flaws. (This doesn't mean that the conversion to analog is flawless, but when you're still in the digital domain you have data that is identical to the original.)

I do have to note that "identical" and "original data" may not be exactly true. There can be slight differences, but they are smaller than we can perceive. Nothing is perfect, but this comes pretty close.





MarkD

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Re: Transports
« Reply #13 on: 30 Jan 2009, 06:09 pm »
If the zeros and ones aren't recognizeable, or if there were interpolation, how could you ever load a program from a CD? 

My assembler language programming days are behind me, and not on the PC platform, but as an example the mainframe operation code for an unconditional branch instruction is 47F0 in hex.  If you change even one bit of that F, it's no longer an unconditional branch.  If you change even one bit in the 47, it's some different operation entirely, probably some instruction that doesn't even exist.

You couldn't load a program from a CD unless the data can be read reliably. 

mattyturner

Re: Transports
« Reply #14 on: 30 Jan 2009, 07:19 pm »
But a PC cdrom drive reading a program gets to read a bad portion of a CD as many times as it needs to to get it right.
When you're reading music that has to be played back in real time, there many not be enough time to read it perfectly.

That is my understanding anyway.

turkey

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Re: Transports
« Reply #15 on: 30 Jan 2009, 08:30 pm »
But a PC cdrom drive reading a program gets to read a bad portion of a CD as many times as it needs to to get it right.
When you're reading music that has to be played back in real time, there many not be enough time to read it perfectly.

That is my understanding anyway.

Correct.

If the data is not read correctly, error correction fixes it fully. Or else it doesn't, in which case you hear artifacts as I mentioned before.