Studio Technologies 78 2004 - Manual (Page 36)

Issue 5, January 2004 Model 78/79 User Guide
Page 36 Studio Technologies, Inc.
for Surround
possible for a slight “tick” to be heard in
the monitor output channels. This is due
to the ‘2310 changing gain circuitry at this
point in its 127.5 dB level range. This audio
anomaly should pose absolutely no prob-
lem during operation. Virtually any audio
signal present will mask this slight imper-
fection. Other than this small issue, the
sonic quality of the ’2310 is excellent—
otherwise it would not have been selected
for the Model 78!
Downmix Formulas
The following provides a summary of
the action performed when the downmix
modes are active. Signals at unity gain un-
less noted. 0.707 = –3 dB; –0.707 = –3 dB
with polarity reverse; 1.414 = +3 dB.
Downmix 5.1 (7.1 to 5.1)
SL = SL + BL
SR = SR + BR
BL and BR mute
Downmix LCRS (7.1 to LCRS)
SL = 0.707(SL + SR + BL + BR)
SR = 0.707(SL + SR + BL + BR)
BL, BR, and LFE mute
Downmix Stereo (7.1 to Stereo)
Configured for Mode 1
L = L + 0.707C + –0.707(SL + SR + BL
+ BR)
R = R + 0.707C + 0.707(SL + SR + BL
+ BR)
C, SL, SR, BL, BR, and LFE mute
Configured for Mode 2
L = L + 0.707C + 0.707(SL + SR + BL
+ BR)
R = R + 0.707C + 0.707(SL + SR + BL
+ BR)
C, SL, SR, BL, BR, and LFE mute
Downmix Mono (7.1 to Mono)
Configured for Mode 1
C = L + R + 1.414C
L, R, SL, SR, BL, BR, and LFE mute
Configured for Mode 2
C = L + R + 1.414C + 0.707(SL + SR + BL
+ BR)
L, R, SL, SR, BL, BR, and LFE mute
Definition of Level—dBu
and dBV
Whenever possible, Studio Technologies
has opted to use the dBu designation as
it seems to be quite rational. Using dBm
was fine when all audio line outputs were
terminated with 600 ohm loads. In this way
it was easy to say that 0 dBm is 1 milliwatt
dissipated in the known load (i.e., 0 dBm
across 600 ohms will measure 0.775 V).
In contemporary situations an output is
rarely terminated with 600 ohms; generally
10 k ohms or higher. The dBu designation
is better because it refers to dB referenced
to 0.775 V, with no reference to load
impedance. This takes into account today’s
audio scene where signals have a low
source impedance, and a high input im-
pedance. The dBu designation is becoming
the standard for the professional audio
industry.
The Model 78 is designed to interface
with audio signals that have nominal sig-
nal levels of –12 dBV to +6 dBu. You might
wonder why “dBV” came into the picture.
Most people don’t realize that equipment
that utilizes “–10” levels usually mean
–10 dBV—substantially different from
–10 dBu (–10 dBV = –7.78 dBu). The dBV
designation is simply a different way of
measuring signal level and is often used
when dealing with portable or consumer