[Harry Lavo]

"Soundhaspriority" wrote in message
...

"Harry Lavo" wrote in message
. ..

"Soundhaspriority" wrote in message
...

"Harry Lavo" wrote in message
...

"Soundhaspriority" wrote in message
...

"Kalman Rubinson" wrote in message
...
On Sun, 22 Oct 2006 15:08:43 -0400, "Soundhaspriority"
wrote:

Lately, I've been hearing that SACD multichannel has virtue, and you
mentioned an ITU standard for speaker placement.

I would appreciate web links or publications.

The full designation is ITU-R BS.775-1 and you can Google it for tons
of info about it. Unfortunately, the document itself costs $ to
download.

Kal

Thank you. Are there any free sources of information on the changes in
recording technique you mentioned, or are they best covered in the
document?

This Friday evening, I'm recording a vintage jazz group in a club in
the Village with very fine equipment. It occurs to me that I could
make a stab at producing masters suitable for multichannel at a later
point -- if I knew how to do it. The plan is to record four channels
at 88/24, but it could be expanded to six without too much additional
overhead.

Is there anything I could quickly grab ahold of?

As a starter, set up an ORTF or XY pair (the ORTF would be better, if
equally convenient) on a stand right behind (e.g. one or two feet) the
main microphones and facing rearward, pointing up at about a 45 degree
angle to face the "null" towards the front of the room. Record the
pair to separate tracks. Mix and match to taste.
That's a very interesting idea. I was thinking of a second XY mic, but
you're right, the ORTF would provide additional spaciousness. However,
in the case of cardioid, as opposed to a hypercardioid, the null is
directly rearward of the mic, which seems to imply it should face
directly away from the performers. It is the hypercardioid which has the
null off the mic axis. Would you care to clarify on this point?

You are right...I was thinking hypercardioid because they are more
popular nowadays. But the classic ORTF is cardiod, of course, and if
that is what you have...face straight back. I might still keep it
pointed up slightly depending on how high you are flying them, because
most cardioids have an elevated high end, and you don't want to "focus"
too much on clinking glasses, rowdy conversation, etc. But nulling
should be the first and foremost consideration.
Your sugggestion is most plausible, but may I ask, have you actually tried
this?

A very quick experiment back in 2002 with a grand piano in a good sounding
room...but it seemed to work okay.

Here's my concern: The distance between the direct mike and the ambient
mike is very close. Quoting the Three-to-One Rule invented by Lou
Burroughs, from "The New Stereo Sound Book":
"If two or more microphones are used to pick up two or more subjects, each
microphone must be at least three times the distance from any other
microphone as it is from its own subject."

The three-one rule assumes that the mics are either omni or cardiods both
facing the same sound source. It's purpose is to avoid comb filtering of
high and upper mid range frequencies, which make your recording sound as if
it is being done on kazoos, or via a tissue paper stretched over a comb
(believe me, you will recognize it if you get it). Because you are
"nulling" both the rear and the front mics when you properly positioning the
rears, you are reducing their output relative to one another by about
20-30db. This basically avoids or dramatically reduces the comb filtering
by iteself. If at all possible, some time to experiment with your exact mic
placement would be useful. You could try to move the mics from 2' to about
6' back behind the front mics and judge the sound by mixing back and front
channels temporarily. Nobody has yet "written the book" on multichannel
recording techniques, other than the work done on ambisonics.

This, of course, assumes that the two microphones are mixed in at equal
levels, the purpose to ensure that comb filters are 10 dB below the
unmixed levels. Perhaps the ambient mic is to be mixed at a lower level.
However, for any level of the ambient mix, an adjusted variant of the
Three-to-One Rule applies.

The final mixing level is something that needs to be done with a control
room or monitor setup approximating the ITU standard. But recorded at the
same level as the front mics, the sound of the rears will automatically be
reduced in level because it will largely be simply picking up reflected
sound and ambience. If audience noise is too great you will want to reduce
it though, in all probability.

If it doesn't work for you, you can always just eliminate the rears, or mix
them in at very low levels to a straight stereo recording.



Comments welcome.

Bob Morein
Dresher, PA
(215) 646-4894