Re: M/S recording on a feature.

On Mon, 6 Aug 2007 21:31:21 -0400, Gtrew wrote
(in article <1186450281.315266.141150@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>):

Stereo dialogue recording for TV/Film production? My cue to stir
things up a bit:

I believe it should happen and my hope is that it eventually will.
Why? A more natural stereo Left-Right image is much easier to listen
to than panned mono dialog.

I think fears about Left-Right positioning of the sound image are
invalid. Just like "crossing the line" for the visual perspective, the
"line" can be established for the stereo Left-Right image. Establish
"the line" and maintain the stereo image as much as reasonable.

It's not really cutting new ground. As I recall, UK production seems
to have done the most with stereo dialog. Would be good to hear from
some of those who remember doing it.

Glen Trew

In 1999 I reviewed a 2-channel LaFont preamp. During the review I talked to
the maker. He said, in France, it was not unusual to record foley in M/S. The
review follows...

The LaFont LP-21 Dual Microphone amplifier

Ty Ford

The LaFont Dual Microphone amplifier ($1,495) is an AC-powered,
transformerless, two-channel, solid state mic preamp with a discrete front
end. Before you dismiss it as another in the cavalcade of solid state
preamps, I should mention that it comes rigged for M/S (mid/side) recording.
You can use either or both channels independently, or together with a
cardioid and figure of eight mic for M/S. (Some have experimented with omni
and hypercardioid patterns instead of the cardioid. The results vary by mic,
source and acoustical environment.)

In the US, M/S is routinely used in the recording of film sound ambience, not
dialog. Briefly, M/S recording involves recording a cardioid mic aimed at the
sound source to one channel and a figure of eight mic aimed sideways (null to
the source) to another channel. The mics are placed with capsules, one on top
of the other, to minimize phase differences. Back at the studio, an M/S
matrix box makes three channels out of the two. The cardioid is the mid or
mono channel. The figure of eight signal is sent to the left channel and a
reversed-polarity figure of eight signal is sent to the right channel. On the
console, the left and right channels are each panned to their respective
extremes. Listening in stereo, the cardioid mic provides the mid channel
(mono) signal. As the two side channels are brought up, the stereo spreads
out increasingly. Because the mics are placed as coincidently as possible, a
stereo recording will survive being reduced to mono, showing only minimal, if
any, phase cancellation.

After the director has decided whether the shot will be a closeup, medium or
wide shot, the mixer adjusts the degree of stereo width of the shot to
complete the aural vision of the director. Extreme closeups with really wide
stereo can be disconcerting. Panavistic wide shots demand more than a narrow
slice of audio. However, all of this is done in post production at line
level.

In a trans-atlantic chat I had with Jean-Pierre LaFont, he explained that, in
France, Foley effects are frequently recorded in stereo. In many cases, by
the time the production is ready for Foley effects, the shots have been
determined. The Foley artist is looking at a rough cut of the footage while
he or she creates the sounds that accompany the scene. The LP-21 is used to
record in stereo on the Foley stage. That stereo could be a sound centered in
a stereo ambience, to one side, or moving through the stereo field to match
the motion on the screen. Being able to quickly change widths and the balance
between stereo field and center channel allows the work to get done more
quickly.

Both preamps of the LP-21 are identical, with both fine and coarse
continuously variable gain knobs, a polarity reversal switch, 20dB pad, 48V
phantom switch, a switchable filter section with both 12dB/octave high pass
and low pass filters, a channel on (or mute) button and an eleven LED output
display with a 13th clip LED. There is no input clip light, but you'll
probably have problems downstream of the output before the input clips. To
the right of these two sections; the Midside Stereophony controls include a
M/S mode switch, width control and center gain control.

Standard gain settings range from 20dB to 65dB. The circuit is designed for
23dB to 25dB above 0dB before clipping the output. There's also a high-gain
button on each preamp that adds another 10dB, making the range 20dB to 75dB.
The 20dB pad before the preamp is designed not to changed the 1.2k Ohm input
impedance of the preamps. Impedance-altering pads usually change the sound of
the mic because they alter the impedance relationship of the mic and preamp
input.

The channel I/O button operates silently, muting each channel. As long as the
filter section buttons are engaged or disengaged quickly, they are also
silent. The high-pass filter is adjustable from 35Hz to 65Hz. The low-pass
filter goes from 1kHz to 20kHz. Maximum output is +27.5dB. Frequency response
is listed at 10Hz to 25.3 kHz (-1dB) and 7Hz to 50kHz (-3dB). Mic amp noise
is listed as -52.2dB @200 Ohms (22Hz-22kHz) at 75.5dB gain. EIN is -127.8dB,
131 dB shorted.

The back panel features two XLR mic inputs, three line level outputs (M-S,
M+S, Mono), a TRS jack for an external mute switch for the two channels and a
jack for a 10-pin HE10 cable for consoles with logic circuits for operating
the channel mutes. This simple but useful feature can be used to mute the
monitors in studios with mics and monitors in the same room. There's also a
standard IEC power jack on the back.

HOW DOES IT SOUND
In the noise test with the RCA 77DX, the LP-21 did as well as most good
preamps with transformerless inputs. For quiet sources, especially with low
level ribbon mics, you will hear preamp noise. The low-pass and high-pass
filters did come in handy for taming unwanted frequencies without noticeable
phase smearing.


I compared for sound, the LP-21 preamps with my GML preamps and those in the
new Mackie VLZ/XDR, through a 1604 VLZ/XDR mixer. The XDR preamps sound
darker and smoother than all previous Mackie preamps I've heard. The GML was
the most natural sounding, the LP-21 a bit more bright, and the XDR brighter
still.

In the quiet of the studio I plugged in a set of Sony 7506 phones and cranked
up a new pair of Neumann TLM 103s with Gotham GAC-3 mic cable in search of
preamp noise. In order to hear the noise, the gain was loud for the Neumann's
to plainly pick up the sound of my lunch of leftover Indian food making its
way through my upper intestines from a distance of about two feet. At that
level, both the GML and XDR preamps appeared to have similar amounts of
noise, which was slightly less than that of the LP-21. I switched mics,
re-balanced gains and tried different inputs, but the noise differences
remained the same on both channels of the LP-21.

I set up for M/S using a Neumann U 89 and a TLM 103 and connected the three
outputs of the LP-21 to the VLZ/XDR, panning both side channels to their
extremes, and bringing all faders up to unity gain. Because the side mic is
90 degrees off axis from the sound, thereby only getting sound as it skips
across the diaphragm, you'll want to use the quietest and best figure of
eight you can get. Otherwise, as you increase the stereo spread, you'll begin
to hear the self noise of the mic. I positioned the mics to keep the figure
of eight from nearby reflective surfaces to keep it from hearing bounced
sound that would mess with the stereo spectrum.

I recorded acoustic guitar at different distances; three feet , two feet and
a foot or less. As I got closer I realized that I could "center" the guitar
so that it nulled out much of the proximity effect caused by having a guitar
sound hole within a foot of the mid TLM 103. When I moved the guitar slightly
to the left or right, the proximity effect started to emerge on the
respective side. Using the width control on the LP-21, I was able to go from
mono to a very wide guitar, filling both speakers. When I pushed the width
control to extremes, I got V e r y W i d e S o u n d and, finally, an
increase in noise.

The next application was to try to record a guitar duo. The thought being,
making a simple stereo recording of two acoustic guitars sometimes gets
really complicated and "phasey" when multiple mics are used on each guitar.
Guitarist Bob Showacre and I formed a more or less equilateral triangle with
the M/S mic array, each of us from about 18 inches to over several feet from
the mics. Placement and movement have a major bearing on where the sound ends
up on the stereo spectrum. At one point, the midrange tones of my D28S Martin
came from more or less the center of the stereo spectrum, while the higher
notes came more from the right side. And that was without moving the body. I
was very pleased with how quiet the recordings were and how natural they
sounded; just a couple of guitars in a nice space. Summing the channels to
mono revealed that the phase anomalies were not great enough to compromise
the high-frequency response. Summing did seem to cause a very slight increase
in upper bass or lower midrange.

I decided to push the envelope a bit by adding a third guitar; a Telecaster
played by my wife Bette. It was plugged into a Fender Super Reverb a good
seven or eight feet to one side of the M/S array. Bob moved slightly more
on-center to allow the Telecaster to fill up the right side. The Tele sounded
"in the room and over to the side somewhere". The hazard of this approach is
that you do lock yourself into the placement on the stereo spectrum and that
everyone playing must be very conscious of the dynamics and levels of
everyone else. If you get it right, it sounds pretty sweet.

IN CONCLUSION
Although the LP-21 was not designed for the music studio, it performed rather
well. If stereo Foley is your bag, the LP-21 is a natural; that's what it was
designed for. Regardless of its minor noise, which I had to dig deeply to
find, it offers two nice sounding preamps, filters, and the all important M/S
matrix controls. It'd be nice to have a line level input to matrix M/S
recordings, but you can do that with three inputs and one polarity-reverse
switch or cord. I wanted to record a drum kit, thinking M/S would sound great
on the right drums with the right player in the right room, but I ran out
time and words. Hey, make that your next project.

Technique, Inc. (C) Copyright 1999. Ty Ford may be reached at www.tyford.com.

PRO: M/S matrix and filters are a plus.
CON: Slightly more expensive due to added features.
APP: Foley and other stereo or two channel recording.


--Audio Equipment Reviews Audio Production Services
Acting and Voiceover Demos http://www.tyford.com
Guitar player?:http://www.youtube.com/watch?v=4RZJ9MptZmU

.