Optimal length for digital cables: 1m or 1.5m?

First, I'm not sure why you would be using a digital cable between a DAC and a preamp. Usually the left and right channel analog outputs of a DAC would be connected to analog inputs of the preamp, and the cables would be conducting analog signals.

In any event, assuming that the cable is conducting a digital signal, yes 1.5 meters would be a safer choice. See this paper for an explanation. Your chances of getting comparably good results with a 1 meter length are dependent on many technical parameters of the specific components that are being connected, many of which are not usually specified by the manufacturers. The particular cable type is also a factor.

So I would suggest that you indicate the make and model of the particular components that you want to connect, and that you do not attach much significance to experiences with 1 meter lengths that may be reported unless those experiences were with the same components.

Regards,
-- Al

I agree with AL. A friend of mine and I have a/b'd a 1 meter Shunyata Zitron Python digital cable and a 1.5 meter Moray James cable and we both preferred the Shunyata cable but we both understand this does not answer your fundamental question. I faced the same cost conundrum you are considering and opted to spend the extra money elsewhere in my system. The only way to know for sure is to compare the two lengths of the same cable with the same equipment, IMHO.

Mea culpa Al! I meant between my Cary 306 that I use as transporter and the Eastern Electric MiniMax DAC Plus (which fortunately has the BNC connector as well). Thanks for the link.

If I may ask you a similar question but for the analogue signal xfer: assuming that there is no impedance mismatch between the preamp and power amp, how short can a RCA interconnect be?

the length that 'supplies' sufficient rated impedance.

If I may ask you a similar question but for the analogue signal xfer: assuming that there is no impedance mismatch between the preamp and power amp, how short can a RCA interconnect be?

If the goal is to minimize the sonic effects of an analog cable, the shorter the better. That may not always be subjectively preferable, though.

The technical factors that are involved in digital signal transmission, and in analog transmission at audio frequencies, are very different. The result being that length considerations for the two kinds of cables are also very different.

I should add, btw, that if a very short length is practical for a digital cable, such as 6 to 8 inches or so, that would often be a good choice. It is the intermediate lengths, that are significantly longer than that but significantly shorter than 1.5 meters, which stand the greatest chance of not being optimal.

Regards,
-- Al

if a very short length is practical for a digital cable, such as 6 to 8 inches or so, that would often be a good choice.

That's interesting info!
Thanks

There in NO one ideal cable lenght. The 'ideal' lenght will depend on the following parameters:

- cable design (with the speed at which the signal travels through the cable beeing the determining factor)
- sampling ratę of the signal beeing sent (there will bedifferent 'ideal' cable lenght for 44.1 and 192kHz files)
- rise time of the digital signal (your transport)

As you can see, even a cable designer have no control over point 2 and 3.