[78-L] Acoustic recording

[DanKj]

  Many of my instrumental Pathe records sound oddly "backwards" (Sergeant Legget cornet solos, especially;  is this what 
we're talking about?  (I can only describe it as MMahh MMahh MMaah as opposed to Wahh Wahh Wahh)


----- Original Message ----- 
From: "DAVID BURNHAM" <burnhamd at rogers.com>
To: <78-L at 78online.com>
Sent: Saturday, July 02, 2011 12:59 AM
Subject: [78-L] Acoustic recording



On Tue, 2011-06-28 at 08:35 -0700, DAVID BURNHAM wrote:
> Does anyone know if, when recording acoustically, the sound was applied to the side of the cutting diaphragm facing the 
> edge of the record or the side facing the centre spindle?

Michael Shoshani responded:


Engravings of Berliner's experimental apparatus show the recording
funnel hitting the diaphragm on the side facing the edge of the record,
and I would presume that that's the way it stayed.

Not only is that easier to work with (the diaphragm input isn't
suspended over the wax), it also ensures that the playback is in phase,
since the reproducing diaphragm will send its output through the spindle
side. Thus, it's as though the original sound wave simply passed
through, preserving the peaks and troughs rather than inverting them.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This was precisely the point I was trying to sort out - whether or not the lateral acoustic pioneers were concerned with 
phase. I know Thomas Edison maintained proper phase by inserting a lever between the playback stylus and the diaphragm, but 
I wasn't sure if lateral cut records addressed the issue.

Absolute phase or polarity as it's sometime's known, is realized when the phase of the reproduced sound in a listening 
environment is the same as the phase in the original performance room, (so that if a compression of air left an instrument, 
the same wave at the listener will also be a compression of air, (this has nothing to do with relative speaker phase which 
most audio techs are familiar with). Absolute phase is so important to the quality of reproduced sound but it appears that 
once electrical recording was introduced, it was no longer considered relevant. Generally, in vacuum tube amps, the phase 
reverses with every stage of amplification. I have seen consoles by Neve where the phase reversed if EQ was introduced in a 
mike channel. If bi-directional, (ribbon), mikes have both front and back employed to pick up sources, those hitting the 
rear of the mike will have their phase reversed. Now it appears that audiophiles are once again
 becoming aware of the quality improvement from correct absolute phase and many seem to think it's a new discovery, Charles 
Wood, at the Defense Research Labratory in 1957, wrote an article about the situation and even gave his own name to the 
phenomenon, "The Wood Effect". It is very difficult to check that a recording is being reproduced in correct absolute phase. 
Often, it's a case of playing a section of a record, turning everything off and reversing the wires to each speaker, then 
listening to the same recording again. It's hard for the ear to remember the subtleties of the sound for the length of time 
it takes to do that; and since phase varies from recording to recording, you'd have to go through that for every record if 
you always want to hear the correct phase. Some preamps, (like the Bryston model I use), have a remote controlled phase 
reverse switch which makes the whole process much easier.

But it's nice to know that the acoustic recording pioneers were aware of the importance of phase and, probably without even 
thinking about it, made sure that every recording was in the correct phase or polarity. Nobody would think that it doesn't 
matter if you look at a black and white photograph as a positive or a negative - yet an out of phase audio wave is the same 
as a photographic negative.

db
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