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Multi-CD players/transports...


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I really enjoy the convenience of having several CD's available for random playback at any one time, but I understand that there is a level of detail provided by high-end, single-CD players that most multi-CD players cannot reach. Is the reason for this gap in playback quality at all due to the quality of the transport devices? Or is the quality of the digital to analog converter the biggest culprit?

As such, are there any multi-CD players/transports available out there that can be used alone or in conjunction with a separate DAC that will deliver the detail, timing and overall quality found in high-end single-CD players/transports?

Any help would be greatly appreciated. I am well aware that these differences would only be apparent in a system that can bring out such differences, so let's all assume that isn't a problem. I KNOW those differences can be quite dramatic, because I've heard two different CD-players (JVC and Arcam) matched to the same components in the same room and the difference was quite pronounced.

Thanks for the beta! cwm16.gif

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May the bridges we burn light our way....

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I'm not sure why the transport portion of a cd player should make a significant difference. I remember one of the big selling points for digital audio was it's relative immunity to those sorts of things. Perhaps someone here can enlighten me.

On you subject of multi vs single player choices. Why not find the best sounding multi disc cd player with optical outputs. That way you can later purchase and use a DAC that pleases you while still keeping the fexibility gained by using multi disc players.

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I already use a CD player with a six-disc carousel and an optical digital out, but I don't know whether the quality of transports makes that much of a difference compared to the quality of DAC. If the difference in transports is negligible, I'm set to go with a high-tech DAC. If the quality of transports is wide-ranging and relevant to the sound fidelity, then I'd like to know if there are any good, state-of-the-art multi-disc transports out there. My ignorance is the weakest link in my system....

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May the bridges we burn light our way....

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This is one of those topics that really get some people going. The high-end audio press, particulary Stereophile, The Absolute Sound, Ultimate Audio, Positive Feedback and some others absolutely INSIST that ALL transports make a difference, some more than others (both good and bad). WHY this ought to be true, particularly when talking about a DAC that uses some sort of phase-locked-loop mechanism to latch onto the signal, is a topic that I am in no way qualified to comment upon. Other magazines, like The $ensible $ound, Sound and Vision, and a few others insist that it is ABSOLUTELY IMPOSSIBLE TO DETECT ANY DIFFERENCE BETWEEN TRANSPORTS, under controlled conditions, and that anyone who claimes otherwise is blowing smoke.

I think the only way you're going to get an answer to this that satisfies YOU is to find a dealer who's got a good sense of humor and a willingness to help, and try out some different combinations of transports / DACs, and see if YOU hear a difference.

I, personally, think the quality of the DAC is much more important than the quality of the transport, but who's to say whether I am listening for the same sorts of things that you are? You might find exactly the opposite to be true.

I know that's not much help, but that's my two cents on the issue.

Ray

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Music is art

Audio is engineering

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I agree with what Ray said. I can see that in theory the transport makes a difference. Afterall, it tracks the data from the disc and any vibrations or other anomalies can theoretically create loss of bits. However, does all that really affect the sound quality to an audible level? I don't know the answer to that.

Of course, it's probably possible to build a multi-disc transport that is equal in sound quality to a single disc transport. It's just going to be more expensive.

What I would say is, that you probably will be sacrificing sound quality by buying a multi-disc player. That is, assuming that you have a limited budget to spend on a player. If that is the case, and you can assume that the more you spend on a player, the better player you will get (not always the case of course), then you will get a better sounding player by buying a single disc player. Multiple disc players cost more money, so if you have a set amount of money to spend, some of your money will be going to the multiple-disc feature instead of to improved sound quality. Whether or not the transport itself makes any audible difference, that will be true. That is the reason I will only own single-disc players, cause they will (should) give me more sound quality for the money.

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Here is the skinny:

When looking specifically at a transport, the only thing it must do is provide a sufficiently low Bit Error Rate (BER). When the CD Player gets data off the disc that fails a CRC check, it will interpolate over the missing data to the best of its ability. The more stable a transport is, the more it will be immune to variations in poorly-made discs and such.

That said, any decent quality transport playing a disc that is unscratched will produce a fantastically low BER, (Yes, they do occur, even in super-high-end stuff, but typically they happen with no regularity or anything, and thus don't change the overall sound of a CD-P unless they get really excessive.)

The particular relationship between Transport & DAC gets confused a lot. (Especially if they are inside the same box, a typically CD Player) This is how we end up with those 'Green Pen' or 'Green LED' and other things to try to improve the sound. It HAS BEEN proven that these do not effect the BER, and thus absolutely do not, in any way shape or form whatsoever, have any effect on the data or clock being received by the DAC. (People will say it effects the jitter of the clock, but this is incorrect because that is not how the DAC clock is actually derived.)

The transport need only pull the bits off the disc with a sufficiently low BER. I suppose in THEORY a super-high-end transport will produce a slightly lower BER, but there is no real evidence to support this.

The single most important factor in any digital audio playback system is the clock, second after that is the analog stage after the DAC, third is probably the power supply, and then the DAC, probably.

Super High End transports perform better because of thier clock, but in all honesty, once it has been sent through S/PDIF or TOSLINK or something, you've just thrown that away.

So the very best performing architectures are a single combined CD-P unit (whether or not it is multi-disc is really irrelevant, the clock is most important), or a Transport & DAC combo with the clock located in the DAC, and fed back to the transport, or a system using asynchronous communication (ie Firewire) with the clock located in the DAC.

To make a long story short, a multidisc player is not inherrently inferior, although TYPICALLY they will be (Cost of the mechanism might put a squeese on parts quality elsewhere, etc...)

Charlie

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"What's that noise?" "It's the carpet, it kinda mutes the speakers." "No, it sounded more like the chandalier falling."

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I have been using Pioneer Elite 301 CD changers as transports for quite awhile. I use the DAC in my pre/pro with fairly good results. The only other CD player that I can compare it to is a Marantz 63se single disc player. I could tell no difference between the two as far as sound quality went. I understand that the Marantz isn't a true high end CD player but it was pretty good. I guess my point would be that I haven't felt that I am missing anything by using the mega changer. Actually the Pioneer sounds pretty good using its built in DAC also.

Q.

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disco, I am using an early prototype of an Asynchronous Input DAC (firewire). The audio is ripped from CD onto a small computer (located in the next room from my stereo) and compressed using a lossless format known as FLAC and saved to hard drive.

The data is played back currently via USB to the DAC, which has special isolation to separate the circuits containing the clock & digital filter from the microcontroller which communicates with the computer.

The analog stage is currently two Burr Brown PCM1702 with op-amps from Nat Semi on the output.

This winter/next spring I will rebuild it using firewire and a DVD-Audio and SACD capable DAC chip with transformer-coupled tubed output stage.

Charlie

------------------

"What's that noise?" "It's the carpet, it kinda mutes the speakers." "No, it sounded more like the chandalier falling."

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It looks like the question can be rephrased:

are there any multi-disc transports that can use the clock fed to it from a separate DAC?

However, why would the clock information in the DAC have to be fed back into the transport unit? I thought the DAC derived it's clock information from the disc itself (read: the information being supplied by the transport. Wouldn't be irrelevant to the transport what the clock on the DAC is "saying"?

I have to admit, I'm using this new vocabulary (clock) without having a full understanding of its meaning. So, please be patient with my questions.

I also did not understand, Spider, how using "S/PDIF or TOSLINK or something" could eliminate the benefits of a high-end transport's clock. In fact, why does the transport have to use a clock to begin with; isn't timing of the signal a function solely of the DAC?

All help is greatly appreciated.

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May the bridges we burn light our way....

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Here's how it works:

Digital Audio is made of two things: The Data and the clock. The sampling rate (clock) is how many samples (the data) per second are taken.

A CD Player/DAC system has a single clock somewhere in it. The clock is just a circuit with a timing crystal which creates nice on-off square pulses at about 256 or 512 times the sampling rate (44100 samples/s, so the master clock is usually 11.289Mhz or 22.579Mhz). The chipset for the CD transport takes this clock and compares this clock to the speed of the disc(not RPM, the linear velocity past the lens). It uses this ratio to adjust the speed of the disc so that the data is recovered at the right speed.

< Note: Others (especially 'Green Pen' advocates or 'tweakers') often have this backwards and believe the master clock or DAC clock is derived from the speed of the CD, this is incorrect. >

The transport slightly buffers this data and does interpolation/ error checking as neccesary then converts it to a serial format such as I2S which consists of a Word Clock (It is '1' when sending the left channel, and '0' when sending the right channel, or vice versa, depending on the setup), the Bit Clock (Which toggles from '0' to '1' each time a new bit of data is available), and the Data itself (which is read at the receiving end on every 0->1 transition of the Bit Clock).

Now, where this goes is depends on the setup. In a plain CD Player, these signals are fed straight to the Digital Filter (or DAC if it has an internal Filter). The Digital Filter does some processing to the signal, and then feeds it out to the DAC chip(s). The DAC uses these signals and the master clock to recreate the analog signals. The quality of sound playback is almost completely dominated by the quality of the clock, power supply, DAC, and analog stage.

If it is a Transport, or a CD-Player with digital out that you are using, it goes to a S/PDIF transmitter/encoder. THIS is where the loss of clock information occurs, for the most part. The three signals (word clock, bit clock, data) are encoded onto a signal line using the master clock. They are encoded using BitPhase Mark encoding. Meaning two 0->1 or 1->0 transitions equals a '0' and a single 0->1 or 1->0 transition equals a 1. (Or the other way around, I forget)

The bitphase-mark encoding is decoded by a S/PDIF receiver chip, and it has an internal clock and PLL circuit which 'locks on' to the incoming signal. THIS clock is then used for the DAC. Typically this clock is of considerably lower quality (More jittery, less stable, etc...) than the one coming straight out of the Master Clock in the transport. There are various techniques to improve this (Better power supply for the 'analog' side of the receiver, using a sample-rate converter and other buffering, which would let you use a NEW clock for the DAC chip; all these schemes work well, but fundamentally, you can't create a really good clock and lock it to the incoming data as well as if it was fed directly.) Here, while the DAC chips and analog stage are still important, the quality is totally dependant upon the method used to recover/create the clock.

A trick around this, though is to place a new Master Clock in the DAC, and use this to clock the DAC chip, rather than the clock recovered by the S/PDIF receiver. This clock is then fed back to the transport. Otherwise the transport wouldn't know QUITE how fast to pull the data off the disc and would get off, and skipping or other nasty things would happen. Also some Digital Filters require the Word Clock or Bit Clock to be in proper phase with the master clock (ie, the 0->1 transitions of these signals occur precisely when a 0->1 transition of the master clock occurs)

Unfortunately not all transports & DACs use the same master clock frequencies. Thus while this is sometimes doable, it is the most complex and most difficult to get going.

The way my setup currently works is that the data is read off the CD by a transport, and buffers the data PERMANENTLY (to hard disc) before the 'convert to I2S' phase. The data is then read off the hard disc, and passed to a circuit in the DAC which does the I2S conversion and feeds it directly to the digital filter or DAC chip. The DAC has a large buffer, and when it is about to run out of information to pass to the digital filter, it requests more from the computer. The Computer<->DAC communication occurs at no particular rate and timing of this has no effect on sound. Thus there is one high-quality clock in the DAC, and assuming proper design & layout are used, the clock becomes almost a non-issue, as jitter at the dac chips is about 3-4 pico seconds. (In typical S/PDIF receivers, jitter may be many hundreds of pico seconds, and this is DEFINITELY audible and contributes much to the nasty sound of most digital stuff.)

Hope this has helped somewhat Smile.gif

The best solution is probably to get a CD-Player with the highest-quality changer/transport mechanism, and not worry QUITE so much about sound quality right away. Clock & Analog stage upgrades are available (although you might need help installing them). Also some tweaking of the power supply with better capacitors will have a big impact. *IF* you are willing to tweak, a decent $200-300 multi-disc CD Player with about $200 in tweaks will toast just about any single-disc you could buy for $800-900.

I'm not an electrical engineer and digital audio nut, but I DID sleep at a Holiday Inn Express last night.

Charlie

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It sounds like you got some rest, Spider. Thanks for your thoroughness.

Are there any resources out there that list and explain these upgrades to those of us without the engineering education or a Holiday Inn Express at hand?

I AM willing to tweak and upgrade the CD player, but I suspect the learning curve is steep.

Thanks again.

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May the bridges we burn light our way....

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I would like to recommend you look at the Denon DCM-5000 and 5001. They are excellent, well built CD changers, that sound great.

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Fronts: KLF30's paired with KSW15's.

Center: KLF-C7

Sides: KSP-S6's paired with Pinacle Baby Boomers.

Rears: KLF-20's with one KSW-12 in between.

Denon AVR-5800

Denon DVD-3300 DVD-A with iScan Pro(Prog scan)

Sony KP-53XBR300 TV

Denon DCM5000/DCM5001 CD Changers

Denon CDR-W1500 CDRW

Denon TU-1500RD Tuner

HHB CDR850 Pro CDRW

Tascam DA-302 Dual DAT

ButtKicker/Behringer EX-1200/Carvin DCM-1000

Monster HTS5000/HTS2500

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Well I belong to the other camp. That is, the one that thinks that transports make a difference.

Didn't used to...but do now.

There is one issue not discussed (at least at the level it deserves) in this thread: jitter.

This differs from bit error rate substantially and typically is not a problem with computer based (data) use of CDROMs.

I can say that I hear a difference, a big difference, between a conventional CD player used as transport and a dedicated CD transport from a high end manufacturer.

And then, there's the subject of...digital cable. Yes, Virginia, they do make a difference.

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My CDs sound equally fabulous from either my Sony CX400 changers or from my Sony XA1ES as long as I take the optical output from either and feed it through my new Periferal Technologies P1A digital correction engine (converts 16 bit to 24) reduces "jitter" while the P3A DAC upsamples (44.1kHz to 96kHz). The result is much "bigger sound" - bigger soundstage - fantastic detail and imaging - increased dynamic range - my CDs have become "super" CDs!

Klipschorns w/ ALK crossover upgraades for music

Dynaco PAS-4 pre-amp w/ Tesla tubes

Outlaw 1050 6.1 AV receiver

MSB Digital Director

4 LaScalas (suround, center & rear)

Peripheral Technologies P1A & P2A

3 Sony CX400 changers

Nirvis Slink-e computer interface (controls changers, downloads contents and album covers from internet)

Sony XA1ES CD player

Sony S530 DVD player

Sony 798 HF VCR

Panasonic component video monitor

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"I can say that I hear a difference, a big difference, between a conventional CD player used as transport and a dedicated CD transport from a high end manufacturer.

And then, there's the subject of...digital cable. Yes, Virginia, they do make a difference."

OK, so what was the "big difference" you heard?

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The most obvious example I had was when I went to the Minnesota Orchestra at Orchestra Hall playing Stravinsky's Firebird.

A week later and fresh from that experience, I realized that I had an excerpt recording of Firebird by the MO at OH. Only difference being Oue as conductor instead of a Russian guy who conducted the live show.

At the time, I had two different digital cables: my original cable, a DH Labs Silver Sonic D-75, and an Apogee Wide Eye. The Wide Eye was the current cable in the system. Again, we are talking digital cables here, going between the transport and the DAC.

I listened to the recording and marvelled at how wonderful it sounded. Then, in a fit of A/B madness, I dragged out the DH Labs cable and swapped it for the Apogee.

Two immediately obvious conclusions came from this:

1) the Apogee has a more extended high end to it, almost bright.

2) the DH Labs has a better soundstage, enabling me to identify stage locations for the violins and percussion better than the Apogee.

While I did not think the Apogee overly bright, the soundstaging was important to me, and the DH Labs did not sound "dull", just not as bright, maybe even... right? ... so I left the DH Labs in place.

I have recently completed building a Max Rochlin Ultimate digital cable, and have been breaking it in for the last few weeks.

I will A/B the Max cable with the DH Labs and the Apogee sooner or later and I am fairly confident that it will play well compared to it's competitors.

Does that answer your question?

And yes, we are talking 1's and 0's here, pure and simple.

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Randy, every single time I mentioned the quality of a clock, I was specifically speaking about jitter. Sorry I was not clear on this.

I'll say it again: The quality of a transport in terms of jitter is dependant 100% on the quality of the clock (and it's power supply), NOT the mechanism or laser pickup.

EDIT: What I'm saying here is that a transport, even an extremely high-end one, has no sort of 'inherent' advantage over a regular CD Player, it is completely dependant on the quality of the clock, and the various parts of the DAC (as I said in my post there). A Transport/DAC combo has some advantages (upgrading one at a time) over a single CDP unit. But if the Transport/DAC combo is using S/PDIF or similar, it will almost ALWAYS have worse jitter than a combined unit with a good clock (like the Audiocom Superclock or the LCAudio XO).

Charlie

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"What's that noise?" "It's the carpet, it kinda mutes the speakers." "No, it sounded more like the chandalier falling."

This message has been edited by Spider124 on 07-18-2001 at 05:35 PM

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Right you are Charlie, my mistake.

I sped red your posting and saw the buzz word "computer" there, and interpreted it as a person dealing with data stream issues but not jitter issues. Clearly as you demonstrate the computer cares nothing about jitter, recreating the data stream with binary precision.

I agree completely with your statement regarding clock, power supply, dac, analog stage.

However I am not sure you are free of jitter, except perhaps as induced by the transport. The data stream off the computer suffers from similar compromises, in that a supply rail will lower and raise based upon load, and induce clocking discrepancies. Further, and I am not anything like an expert, I think the dac itself will suffer from self-induced jitter.

The reason I say this is that I proposed a similar solution as you -- except instead of a hard drive, a large enough RAM buffer so that the 16bit words could be reassembled and shuffled off with proper clocking (in the outboard dac) -- which was soundly rebuked as a flawed concept, for the reasons that I listed, as far as memory serves.

There is a company, in the UK I think, that sells a modification to various transports and dacs which basically takes the master clock off the transport and feeds it via another wire into the dac, which then uses that instead of it's own.

This is something I might want to try, although it is in the realm of irreversible tweaks (or close to it).

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