[78-L] Binaural, duophonic, etc.

[Michael Biel]

On 4/20/2011 5:02 PM, DAVID BURNHAM wrote:
> Dan Van Landingham wrote:
>
> "Binaural" refers to a method of recording that mimics the human
> ear. - "Two Sounds." The microphones are literally mounted on a Styrofoam
> head in some cases,

Let me mention again that this use of the word was not solidified until 
the 1960s.  Prior to this binaural was used for just about any 
two-channel recording, including some that have w-i-d-e separation.

>   or a single crossed-8 cardoid stereo mic is used.  The
> listener wears headphones.
>

The explanation below is quite good, but I think that the above 
description might have been mis-understood because the wording is a 
little confusing.  Blumlein and others didn't always use a pair of 
bi-directional with one facing forward and the other facing sidewards.  
Sometimes a cardioid is used facing forward and the bi-directional 
pattern is facing sidewards.  I think this is what is meant in this 
description.  Using a cardioid as the forward facing mic instead of a 
bi-directional reduces pickup from the rear, such as audience noise and 
hall reverberation.   Stereo mics like the AKG C-24allowed for the 
changing of the patterns -- in the case of the C-24 even from the 
control room while listening to the results live!

Mike Biel  mbiel at mbiel.com
> ~~~~~~~~~~~~~~~~~~~
>
> As dl has pointed out, Duophonic was a Capitol term for simulated stereo.
>   Binaural recordings have to be made using microphones spaced approximately the
> same distance apart as the distance between a pair of ears, just like stereo
> photography uses two cameras which are eye-spaced apart.  In both cases the
> signal for the left ear/eye cannot reach the right ear/eye or it won't work.
>   That's why headphones or some sort of glasses must be employed respectively
>
> BUT the second half of the above statement is not only wrong, but is confusing.
>   There are several different kinds of mikes, based on polar patterns;  two of
> these are Cardioid and figure of 8.  Crossed figure of 8, (or bidirectional)
> mics will yield superb stereo recordings reproduced on speakers.  This is known
> as an XY system and was regularly used by BBC and EMI in the early days of
> Stereo.  The system was invented by Alan Blumlein and bears his name.  A
> bidirectional mike is also known as a cosine mike because the level of pickup is
> proportional to the cosine of the angle of incidence on the mike.  This may
> sound confusing but what it means is that this particular pickup is ideal
> because when your position to the mike is 90 degrees, which in an XY system is
> the direction from which the right signal will be arriving to the left channel
> mike, the output is theoretically zero, (the cosine of 90 degrees is "0").  At
> 45 degrees, which is the angle at which each mike will be picking up a centre
> sound source, the output of each mike is reduced by half.  If a speaker walks
> from the extreme left to the extreme right of an XY pair of figure 8s, his voice
> level will not vary and the direction of the image will be identical to his
> position on the sound stage.
>
> Crossed cardioids, on the other hand, produce a less than ideal stereo image.  A
> cardioid mike is only down a couple of dBs at 90 degrees so a signal from the
> right side of the sound stage will produce a considerable signal to the left
> channel mike.  If the same speaker walks across a XY pair of cardioid mikes, the
> image will never be at the extreme left or right and the voice will be louder
> when he is at the centre, (called centre channel build up).
>
> In any case, neither of these situations will produce binaural recordings
> because the inter-channel time difference which is required for binaural
> reproduction is totally absent when using a coincident stereo mike.
>
> db
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