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
>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: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.