On Wed, 11 Mar 2015 20:42:59 GMT, (Don Pearce) wrote:

On Wed, 11 Mar 2015 19:46:25 GMT, (Don Pearce) wrote:

On Thu, 12 Mar 2015 06:40:05 +1100, Trevor Wilson
wrote:


**Well, it would, wouldn't it? Phase shift and all that.... The human
hearing system is exquisitely sensitive to phase shift.


The human hearing system is essentially totally deaf to phase shift.
I've seen an experiment in which the phase of the harmonics of a
square wave was cyclically shifted. You could see the waveform
changing shape on a scope. Even with the picture in view, it was
impossible to hear any change in the resulting sound.

Deafness to phase shift is the reason why Orban's Optimod system is
able to operate inaudibly.

d

I've managed to recreate something like it. Have a listen, then look
at the waveform on an audio editor. This will show you how human
hearing deals with phase shift.

http://www.soundthoughts.co.uk/listen/phase.mp3


Nice one, Don.

Back in the day, 40 odd years ago, there was no easy way to produce
such test tones other than comparing input and output signals with a
'scope of a three head tape recorder that would let you switch between
source and replay.

Even then, all you could do was switch between two specific
waveshapes with such a set up. Despite having the necessary kit to do
the test, I was happy to take the author's assertion on trust since it
saved me having to haul a 60 or 70 Lb 'scope up and down the basement
stairs to run the test.

Another fact, of some importance to analogue tape, is our relatively
high tolerance to intermodulation distortion. Even the professional
multi-track studio recorders, running at 30 ips could show routine IM
distortion levels as high as 30% on master tapes.

You can see very sound technical reasons for the practice of direct
cut recording of acetate masters for vinyl reordings. These days, use
of digital recording methods in place of the traditional studio master
tape to recreate such direct cut vinyl records offers the benefits of
tape to vinyl transfer but without any of its deficiencies.

Anyone still catering to this specialist demand for direct cut vinyl,
if they've any understanding of the orginal reasons for using such a
difficult method to make such disks, would simply use a digital
intermediate master and save themselves the grief of an actual direct
cut process - the end result will be indistinguishable from a true
direct cut (other than for the tighter control of the variable groove
pitch with level).
--
J B Good