Re: Help requested on blind cable test

On 28 Nov 2003 15:28:51 GMT, [EMAIL PROTECTED] (Michael Mossey)
wrote:

>I'm about to compare interconnect cables blind.  I'm trying to
>establish for myself whether cable quality is an important factor, and
>whether interconnects of similar construction can vary in subjective
>sound.
>
>I'd like to use two cables that are electrically similar.  Right now I
>own two cables that might be fit for comparison: a 2M Radio Shack
>"gold" special, and a Transparent 2M Link 300.  I thought I would
>measure the capacitance of each cable using this rather cheap meter
>that I own.  Turns out the Radio Shack is 400 pF, and the Transparent
>audio is 280 pF.  Do these numbers sound reasonable?  I'm not sure if
>my meter is working or if I'm doing this correctly.

These are reasonable figures for 2 metre cables.

>And my EE knowledge is rusty.  I want to figure out how this
>capacitance might affect the transfer function.  This interconnect
>runs between a CAL Sigma II DAC and an Audio Research SP-6.  What is
>the impedance of a capacitor again?  Something like 1 / ( 2 * pi *
>frequency * capacitance) ?

The important thing is the output resistance of the DAC, which forms a
low-pass filter in conjunction with the cable capacitance. If it's
less than 300 ohms, there should be no audible treble droop with
either cable.

>Since I suspect that cable quality is real and can be heard blind if
>the test is carried out properly (my theory is that quick switching is
>an improper way to seek out small changes in sound), I'm interested in
>results that would challenge the scientific field of psychoacoustics. 

If that's your theory, then you are indeed challenging a century or
more of psychoacoustics! :-)

>How small a difference in transfer function is considered inaudible?

Typically, 0.5 to 1dB level difference is audible. Freequency droops
are less obvious, you might need as much as 2-3dB at 20kHz to be
audible.
-- 

Stewart Pinkerton | Music is Art - Audio is Engineering