MSP 34x2G
PRELIMINARY DATA SHEET
2.6.4. Application Tips for using 3D-PANORAMA
2.6.4.1. Sweet Spot
Great care has to be taken with systems that use one
common subwoofer: A single loudspeaker cannot
reproduce virtual sound locations. The crossover fre-
quency must be lower than 120 Hz.
Good results are only obtained in a rather close area
along the middle axis between the two loudspeakers:
the sweet spot. Moving away from this position
degrades the effect.
2.6.4.4. Cabinet Requirements
During listening tests at Dolby Laboratories, no reso-
nances in the cabinet should occur.
2.6.4.2. Clipping
Good material to check for resonances are the Dolby
Trailers or other dynamic sound tracks.
For the test at Dolby Labs, it is very important to have
no clipping effects even with worst case signals. That
is, 2 Vrms input signal must not clip. The SCART input
prescale register has to be set to values of max 19hex
(25dec). This is sufficient in terms of clipping.
2.6.5. Input and Output Levels in Dolby Surround
Pro Logic Mode
However, it was found, that by reducing the prescale to
a value lower than 25dec more convincing effects are
generated in case of very high dynamic signals. A
value of 18dec is a good compromise between overall
volume and additional headroom.
The analog inputs are able to accept 2 Vrms input level
without overloading any stage before the volume con-
trol. The nominal input level (input sensitivity) is
350 mV. This gives 15 dB headroom. The scart pres-
cale value should be set to max 0 dB (max 25dec).
Test signals: sine sweep with 2 VRMS; L only, R only,
L&R equal phase, L&R anti phase.
I2S-Inputs should have the same headroom (15 dB)
when entering the MSP 3452G. The highest possible
input level of 0 dBFS is accepted without internal over-
flow. The I2S-prescale value should be set to 0 dB
(16dec).
Listening tests: Dolby Trailers (train trailer, city trailer,
canyon trailer...)
With higher prescale values lower input sensitivities
can be accommodated. A higher input sensitivity is not
possible, because at least 15 dB headroom is required
for every input according to the Dolby specifications.
2.6.4.3. Loudspeaker Requirements
The loudspeakers used and their positioning inside the
TV set will greatly influence the performance of the vir-
tualizer. The algorithm works with the direct sound
path. Reflected sound waves reduce the effect. So it’s
most important to have as much direct sound as possi-
ble, compared to indirect sound.
A full-scale left only input (2 Vrms) will produce a full-
scale left only output (at 0 dB volume). The typical out-
put level is 1.37 Vrms for DACM_L. The same holds
true for right only signals (1.37 Vrms for DACM_R). A
full-scale input level on both inputs (Lin=Rin=2 Vrms)
will give a center only output with maximum level. The
typical output level is 1.37 Vrms for DACM_C. A full-
scale input level on both inputs (but Lin and Rin with
inverted phases) will give a surround-only signal with
maximum level (1.37 Vrms for DACM_S).
To obtain the approval for a TV set, Dolby Laboratories
require mounting the loudspeakers at the front of the
set. Loudspeakers radiating to the side of the TV set
will not produce convincing effects. Good directionality
of the loudspeakers towards the listener is optimal.
The virtualizer was specially developed for implemen-
tation in TV sets. Even for rather small stereo TV's, suf-
ficient sound effects can be obtained. For small sets,
the loudspeaker placement should be to the side of the
CRT; for large screen sets (or 16:9 sets), mounting the
loudspeakers below the CRT is acceptable (large sep-
aration is preferred, low frequency speakers should be
outmost to avoid cancellation effects). Using external
loudspeakers with a large stereo base will not create
optimal effects.
For reproducing Dolby Pro Logic according to its spec-
ifications, the center and surround outputs must be
amplified by 3 dB with respect to the L and R output
signals. This can be done in two ways:
1. By implementing 3 dB more amplification for center
and surround loudspeaker outputs.
2. By always selecting volume for L and R 3 dB lower
than center and surround. Method 1 is preferable, as
method 2 lowers the achievable SNR for left and right
signals by 3 dB.
The loudspeakers should be able to reproduce a wide
frequency range. The most important frequency range
starts from 160 Hz and ranges up to 5 kHz.
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Micronas
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