Solidyne 462dsp, Руководство пользователя

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SOLIDYNE 462
dsp - broadcast digital processor Page 21
TIPS
•
In order to process voices, use slow recovery time, so that
the AGC can effectively correct differences in the program
signal. Let us analyze an example: the telephone line
arrives with low level. While the speaker in studies speaks,
the AGC works at certain level; when the caller speaks,
the telephone presents less volume on the air, and the
AGC must act fast to correct this situation; increasing its
gain.
When the speaker returns, the AGC will reduce their gain
again. And it will have to act with very little delay. The
hold threshold will have to be low, to avoid that the AGC
“is hooked” freezing their value during the telephone
communication of previous example.
•
The AGC attack and recovery times must be carefully
defined so that its action is not in evidence. If the attack
time is excessively slow, the action of the AGC could
notice (the level reduction can notice). If the recovery time
is very slow and the attack time is very short, when
somebody shouts (a cough, an outburst of laughter) the
AGC reduces its level abruptly and takes soon in
recovering its level. Then the effect will be similar to
“somebody lowered the volume of the radio”.
•
For music, it agrees that the recovery time be slow. If it’s
fast, the dynamic of the music are completely lost.
4.4.2.4 Hold
This is a gated AGC. For this reason, when the input
signal falls abruptly, the AGC does not compensate its
gain, but that congeals their current value; remaining
in that state until the signal exceeds the “hold”
threshold. Otherwise the AGC would compensate the
input level continuously, increasing the background
noise in the pauses; due to the signal absence the
AGC would increase its possible gain to the
maximum. The Gated AGC solves this disadvantage.
Strictly speaking, AGC value is not congealed; but
that slips slowly towards 0 dB; to avoid that it is
hooked if the signal remains with low level (slope =
0.75 dB each 13 seconds; 4.5 minutes from -15 dB).
On the other hand, you can adjust the HOLD
threshold to conserve part of the dynamic range of the
music. That is to say: if a "forte" passage is followed
by a subtle appearance of an instrument, the AGC will
hold its gain level, giving rise to the contrast of
loudness. When the "piano" passage reaches the
HOLD level, the AGC unhold and begins to increase
their gain according to the recovery time.
4.4.2.5 Expander threshold
Change the expander threshold; from -50 dB to -80
dB in steps of 1 dB. This level is referred to 0VU input
(overload level). The threshold is the point from which
the expander begins to reduce its gain, as signal level
is reduced. The object of the expander is to improve
the signal/noise relation on the air. This is because the
multiband compression, although increases the
loudness, reduces relation S/R. This effect would be
annoying, but for the action of the expander.
4.4.3 AUDIO EQ
This stage involves 4 parametric EQ’s that defines
seven fixed equalization curves (only two for FM in
the current firmware version). Turn the JOG to
select the curves. Option OFF disables the EQ.
The influence of this equalization on the sound is
remarkable, since it works on narrow band of
frequencies, whereas the multiband processor
uses more wide bands. That is why the multi-band
does not cancel the action of audio EQ, even with
gains of 3 dB.
Low frequencies
are boosted around
70 Hz
(3dB), to reinforce the deep bass sounds. This
effect is very noticeable in medium and big
loudspeakers.
An
attenuation
centered at
200 Hz
add “air” to the
sound, lowering mid-low components that usually
can produces distortion in small speakers,
generating a confuse sound.
Finally, the curve gives presence and clearly highs
to the sound. This is obtained emphasizing (3 dB)
frequencies around
3 KHz
and
15 KHz
.
Presetting curves are combinations of these four
equalizations (only two are available in the current
firmware version).
Presets
5
,
6
and
7
are for
AM
models.
4.4.4 MULTIBAND COMPRESSOR
The object of the multiband compression is to increase
the energy in the entire audible spectrum. The
theoretical foundations of this technique are explained
in Chapter 6 of the 462dsp user's manual. Next a brief
review of multiband compression offers, and is detailed
soon how different processing adjustments affect to
music and the word.
Remember:
a compressor is basically an amplifier whose gain
changes from a certain level of signal. This change of gain
denominates “compression ratio”. For example, a compressor