@kraftwerkturbo
isn't a transport by definition a 'CD player without DAC', something that reads the digitial informaton on a CD/DVD/SACD (physical media)?
Yes.
Never heard of a 'transport' that 'transports' digital files to a DAC. Unless you refer to a streamer as a 'transport'?
A transport is whatever device directly feeds your DAC. I can't say with 100% certainty that that is an official definition. But whether the data is being transported from a disk, or being transported from a solid state drive, or being transported from a digital-to-digital converter, or from a computer / streamer, to me it is all the same. The above choices differ only in regards to the storage medium that has the bits that get fed / transported to your DAC.
If so, why would I put a 'transport' between computer and SACD?
Do you mean between a computer and an SACD player (one that has an input to be fed by a computer)?
You do not have to do so. But by introducing a stand-alone, purpose built transport / re-clocker between a computer or streamer (streamers are computers of a sort), then that re-clocker has the last word (in a manner of speaking) as to the timing of the bits that your DAC turns into voltage (the birth of the analog signal).
If you use a low-end re-clocker between a quality streamer and DAC, you can do harm to the sound quality. But a quality re-clocker will feed your DAC the best timed bits, resulting in better sound quality.
Computer already has the file the DAC can convert and feed to the analog parts.
Computers do a relatively poor job in the clocking department. They use their CPU cores, which are always crunching numbers for other processes. Even if your computer is 99% idle, it is multi-tasking.
A quality, stand-alone transport does one job, and only one job.
Also, the accuracy of a quality transport's clocking will be more accurate (likely far more accurate) than a computer's clocking.
The best re-clockers have two clocks; one for songs with 44,100 Hz sampling rate and its multiples, and one for 48,000 Hz sampling rate and its multiples.
One of the expenses of building a high quality transport is the rejection rate of the manufactured clocking crystals.
For the truly exceptional quality transports, they will use only the clocking crystals that are the most accurate. I do not know how they test them for accuracy. But they do.
So with a quality transport, you will feed your DAC an uncanny accurately timed bit stream, and your ears will hear the difference.
Also note that computers generate lots of electrical noise. A quality transport box will be designed to not pass that electrical noise to the DAC. Using quality digital cables also helps in rejecting the noise.
