Calculating maximum cable length is a complex task and is never 
accurate. There really is no brick wall in analog--it is just how 
much degradation is acceptable--but digital is another story and it 
has brick walls.

Two parameters affect analog signal transmission in voltage audio systems:
(a) The capacitive reactance of the cable creates a voltage divider 
with the source impedance of the microphone, creating high-frequency roll-off
(b) The capacitive loading of the cable may be beyond the current 
drive capability of the source's output driver. This creates high 
frequency distortions as well as roll-off.

With normal professional balanced audio connections and voltage 
distribution, especially if the driver source impedance is around 60 
ohms, driving 100 m or more of typical cable is easily possible.

Higher impedance circuits, and especially unbalanced ones, should be 
kept short -- typically in the neighbourhood of 3 m or less.

Phono cartridge connections and Nakamichi cassette machine unbalanced 
outputs are especially sensitive to cable loading.

For some additional insight into cable effects and a definition of 
voltage audio distribution, please see my paper on the subject:

You might be better off leaving the A-D converters in the control 
room and running digital signals to the computers (AES/EBU either on 
110 ohm twisted pair or 75 ohm coax). If I were re-building my 
transfer suite, I would consider MADI and local converters for each 
machine. While it is more expensive than wires and patchbays, the 
price differential is narrowing.



At 03:17 PM 2010-01-17, Jan Myren wrote:
>Here is a question I use to discuss with many of my friends:
>What is the maximum length to an audio cable before there will be a loss in
>sound quality?
>This may for instance concern in situations where the sound card and the
>hard disc is placed somewhat away from the turnable set-up, so that there is
>a need for a long audio cable between the output from the phono pre-amp and
>the input to the sound card.
>Do you have any good ideas?

Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information:
Quality tape transfers -- even from hard-to-play tapes.