What is purpose of a cd transport?

Some people say that a certain cd transport is "good." How can one cd transport be "better" than another?
Isn't their job just to hold/play the disc?
Why to transport CDs, I guess!

Seriously, I have never really understood why the separate transport route. I think it is a throwback to the latter stages of the LP era in a way where merely spinning the record at a constant speed without introducing noise from the motor was deemed not good enough. The same ill logic is applied to digital where mountains are made of the molehills of spinning the disc. I would think that designing a CD player as one integrated unit makes way more sense than a mix and match approach. So, I really have no objection, except for the cost aspect, to having two boxes instead of one so long as they are from the same manufacturer and made to work with each other.

Since high-end is all about overbuilding and overcharging, the separate transport is a great way of achieving both.

Posters will surely pipe up saying that they always hear great and good differences with separates. In years gone by others would have given objective reasons why the two box solution is better, but these posters have all died mysterious deaths in the last few years...
Like anything else that spins, such as a turntable, how well it works depends on how well it spins. The better transports spin with less vibration and noise, the circuitry and laser are better, and they more accurately read the disc and send the digital data to be turned into analog sound.
Its job is to properly read the disc and transmit the digital data. Some transports use better parts and are better built and are therefore better at doing that than others.
Go listen and judge for yourself.......
To supplant Rcprince with an example -- some cdr/dvd-r are better than others. Some power supplies are more elaborate than others. Why separate? Good question -- sometimes it;s just a matter of space, sometimes marketing.
Pbb's post wasn't here when I posted. In theory, a well-designed one box player should beat separates, because that's one less interface and a shorter path for the electronic signal. In fact, the original CD players, with the main exception of Sony's state of the art two-box system they came out with (the 703?), were one-box units. Separate DACs came into play from the high-end designers to take advantage of the additional space in the separate box for the better power supplies and analog sections that couldn't fit in (or for pricing reasons weren't put into) the standard CD player's chassis and because the original one-box players didn't sound that great; then companies like TEAC began manufacturing no holds barred transports that were built like tanks and were far better than the cheap mass-market CD player transports. At that point, with no real high end manufacturers involved in the single box CD player business, a separate DAC made more sense to a person who wanted a better-sounding CD playback system. Now, the power supplies, analog sections and transports in the better one-box players are on a par with the better separates and may have tipped the scales the other way, though a well-designed inexpensive DAC (and there are plenty of them) is still a viable alternative for better sound from an inexpensive CD player. I personally have heard differences in some, not all, transports, but I don't really feel they come close to the magnitude of the differences I've heard in DACs.
There are two completely separate parts of digital playback; the reading of the source material and the conversion of that digital data into analog sound. To perfect them both is two separate tasks. Having them together in one box only makes perfection harder to achieve.

If you an expert digital design engineer, what do you know about making a transport? There are a lot of companies that only make the DAC. If you limit yourself to one box players, you are missing a huge part of the market. You are also missing most of the higher end of the market.

Look at turntables. What if the cartridge and phono stage was built perminently onto the turntable? If you wanted to change something you would have to buy a whole new turntable. I don't know any audio person who would consider that an improvement.

That is actually one thing that turns me off to the lower end of the audiophile turntable market. They are all selling plug and play solutions. You have to pay for the cartridge they picked for the turntable. Back in the pre-digital days in the 70s and 80's the cartridge was mostly a separate purchase, even if you were just buying the entry Dual turntable.

Blue Circle just came out with a two box version of their DAC. The very large power supply is in a separate box. So with the transport you have three boxes in total. MSB has had separate power supplies for years (the P1000).
Audio Logic has done the same thing with their DAC in the past (the new MDX version is a one-box DAC)--in fact, their prototype actually had three boxes, one for the DAC circuitry, one for the analog power supply and one for the digital power supply. With my Forsell's air pump, I have four boxes instead of one. My non-audiophile friends roll their eyes a lot. Does it all make a difference? I think so, but in objective terms the difference all of my esoterica makes is probably very little in the grand scheme of playing music, otherwise I could not be moved listening to music on my car radio.
Yeah Rcprince 4 boxes !!!
In the Blue Circle product I mentioned (BC501-OB), the separate power supply while in one box is actually two supplies. There are two umbilical cords between the power supply and the DAC, one the digital supply, the other analog.
That's how the production Audio Logic with the single power supply did it as well. A good design. I sort of miss the separate boxes from the prototype, though, because you could turn off the analog stage (and therefore save tube life) while leaving the digital stage on all the time, which seemed to help it sound better.

Hell, Sugarbrie, my PREAMP is 4 boxes. Where my friends can turn on their receiver with one button and a CD player with another and have music, I have a tuner, a CD transport, a DAC, two preamp power supplies, an active crossover and four amplifiers to turn on to get music (and then I have to wait 6 minutes until the Jadis' auto-muting goes off)! Is it any wonder people view us as "different"?
I love, I love it, Rcprince !!!!

If you listen to vinyl then you have to get the Blue Circle BC27pi phono stage, even if only for the reason it's a two box phono stage !!

Do you have separate mono-block amps ??
6 separate cables for each tri-wire speaker?

Then install dedicated AC power lines for each power cord !!

Sorry, I am getting out of control here...
The purpose is to transmit digital data to the DA convertor for processing.

A good cd transport definitely make a difference as compared to an average one.

Of course, you can said that a CD transport with a DAC will definitely beat a 1 box player provided that u are comparing in the same class which will cost more.

My advise is still keep to a 1 box player. A CD transport with a DAC sill required a good interconnect & power cable matching in order to sound good.

Sometimes, making thing complicated is a long way to achieve good sound. Keeping your stuff as simple ( CD player, int. amp & speaker ) as it is will be more easier for u to achieve a good sound unless u don't mind spending $$$.

There is another big reason that hasn't been mentioned yet. With digital processors, such as digital EQ and upsampling, or processors built into to surround processors (such as room correction and surround processing), you're better off keeping the signal in the digital domain without introducing multiple DA & AD conversions. You can use the digital out of a CD Player, but why use that if the CD player's DACS will never be used? My preference is to use a high quality transport routed to a Digital EQ processor, then a DAC, then on to the preamp.
Heck, Sugarbrie, for vinyl I only have the Lamm phono to turn on for the phono stage (maybe I should consider the Blue Circle, though the Lamm is really an extra box itself because my Jadis has its own world-class phono stage), but then I also have to turn on the Walker Motor Drive, the Basis' motor and the vacuum for the vacuum holddown! And you guessed the monbloc amps, with two biwires for the highs and a lonely single wire for the bass. I won't go into the four dedicated lines....

Honestly, Jeremy's right, simpler is better if it's well-designed and executed.
The other posters have addressed the "techno" part of your question, I would just like to share I have tried different reference transports and they do offer different sonic signatures just like high end turntables.

I have had in my system the following transports: 1) ML 31.5 2) CEC TL-1 3) Ensemble reference. Each had its virtues and did offer overall sonics that affected the overall signature of my system.

For more details regarding what these differences were you could go to a thread entitled: Reference DACS: An overall perspective.
CD data is encoded using Reed-Solomon error correction. The job of the transport is to read the bits (1's and 0's pits/no pits) off the disk including the additional data for error correction and place it all into a buffer for software error correction and for eventual feed to a DAC.

After error correction the result is two channels of 65536 bit word data streams at 44.1 KHz or a data stream rate of 1411200 bits/sec.

There is not much rocket science to this and, as it is all digital, the data will either be correct or incorrect. Incorrect words will cause skipping of the sound as their remains a gap or blank in the data stream.

The relative difference in transports therefore will be related to how easily it skips and how robustly it reads all the words from say a scratched or damaged disk.

The output bitstream from one transport to another should therefore be the same provided there are no skips.

It is downstream of the transport itself where differences can occur. The DAC conversion requires an accurate clock speed to clock out the buffer and very slight (often inaudible) differences can occur due to different DAC designs/specifications/quality, such as immunity to clock jitter. Things like filters, over sampling, one bit sampling, and multi-bit sampling are all methods to achieve the most accurate conversion and all have advantages/disadvantages and can cause slight differences in the ANALOG output. These differences occur in the DAC after the buffer data from the transport.

The quality of the transport itself should not normally make a difference in the quality of the output provided it is capable of properly reading the bits from the CD. It would require a very bad transport design or a very badly damaged disk in order for the system to fail to get all the correct words off a CD disk under normal conditions.
Yes all CD player/transports can read the data, but the problem is timing and distortion. Imagine what happens to the sound if the speed of the data flow is off and/or it fluxuates because of vibration, irregular speed of the platter, poor cabling, and/or fluxuations from an inadequate power supply (and a little of "all of the above" at the same time).

The data correction in the DAC can only do so much, and of course the quality of the DAC affects this also.
Speed of data flow is related to the accuracy of the clock on the data buffer being clocked out to the DAC....so it is not related to the transport itself as in a conventional turntable...as the buffer makes a disconnect in the flow of bits. Think of the buffer as a hot water storage tank in your home - the boiler/heaters job is to keep it with enough hot water for your needs and then the speed of flow is controlled by your faucets. The transport job is to read the bits accurately from the CD and at speed that ensures the buffer does not empty.
Thanks for the info Shardorne. I've often had trouble finding something that makes logical sense in the audioworld... ;-) I've heard the argument that a transport reads a 1 or a 0 and the distance between them make the note (or is subject to error) - like an analogue record player. This is a digital medium, not an etched vinyl record. Wow and flutter shouldn't affect the digital signal to the DAC when it has correction data, right? It would be great to be located somewhere with enough equipment that I could just sit down and blind compare a discman (assuming it had digital out) and a krell transport to the same DAC.

You are correct - transport wow and flutter do not matter. It can run at any speed as long as it is fast enough to ensure the digital buffer does not run out. Just as you will not run out of hot water if your boiler/heater tops up the hot water quickly enough.

As for a discman digital out....yes it should be as good as the best...after all it is digital and that is the beauty of digital...digital preserves the original data perfectly.

A caveat, this is provided the DAC conversion is using its own digital ref clock to clock out the buffered bits and not slave to the clock signal from the discman....the discman clock might be less robust than a high quality DAC. A variable clock signal gives jitter and therefore distortion in some rare cases (badly designed equipment)

See this link for a good overview

Does the apple airport express provide a quick enough & accurate digital signal for DAC purposes?
Thanks Shadorne. It's refreshiing to read such interesting posts especially your link. I get tired of reading repackaged marketing goop masquerading as fact. - Jim

I have no doubt that the digital output from the Airport Express will be perfectly faithful to the digital data that it receives from a PC. The analog output, however, is unlikely to be as top notch as you might get with an expensive DAC or CD player, but probably good enough for most needs; like feeding various built in speaker zones in a "smart" home (I use my Airport Express to feed a Russound Amp in my utility/boiler room, which feeds five separate house zones).

Here is a link about the airport express


...perfect performance with 16 bit 44.1 Khz digital out (standard CD digital)
Does the apple airport express provide a quick enough & accurate digital signal for DAC purposes?
In my system, it certainly sounds like it does.

For a published, numbers-based opinion, go to Stereophile's website and search on Airport Express for a 2005 John Atkinson commentary. He says the AX output is bit-by-bit identical to an original WAV file. (Note that this also means Apple Lossless compression is bit-perfect, since iTunes streams everything to AX in AL compressed format.)
Thanks for the link Shadorne. I think I'm going to go for that and then find a DAC to run it through. I keep reading about the death of CD and it seems that I'll be content with digital for convienience and analogue for quality. Now I just need to find a reasonable DAC - it seems that audio mirror da-1 isn't listed for sale anymore.
I love this post. In the beginning there is an abundance of reasoning and theory as to how a transport will affect the output sound...and then along comes someone with actual information (Shadorne) and the thread ends abruptly!

I do love the rich language that people use to describe the vague sonic minutiae that they hear from switching components, and I also love when people hear those differences when it may be physically impossible to do so! It's not a bad thing, because if our perceived listening is a combination of physical vibrations as well as psychological influences, then one can be affected without the other and our perceived listening will still improve. And anything that improves perceived listening is a good thing whether it's a glass of wine, an upgraded component, or a nice breeze.

Listening is influenced by so many things, and if getting an expensive transport lets me perceive my music in a more enjoyable way, then in effect that transport actually made my music sound better (to me)!