Solidyne 562dsp, User Manual

Page: 35 / 44

SOLIDYNE 562
dsp - broadcast digital processor Page 35
2.2.6 GATED AGC
This stage constitutes a digital compressor AGC
type (Automatic Gain Control) with its constants
(slow) based on the program signal. This
adjustment is made having in mind the
psychoacoustics criteria before explained. This is
very important since the AGC is a wide band
compressor; the ear tends to note its action due to
the modulation that bass frequencies produce in
the highs. In order to avoid it, the AGC time
constants are carefully controlled. Still more; we
cannot speak of attack or recovery times in strict
form, but a
curve of control, s ince the form of the
attack or recovery ramp is controlled according to
these criteria
Otra característica importante de este compresor
es que su recuperación es GATILLADA. Es decir
que solamente acciona en presencia de señal de
programa. Cuando el nivel de programa cae por
debajo de cierto umbral con respecto al nivel de
salida del AGC, la recuperación es cancelada y el
compresor permanece exactamente con la misma
ganancia que tenía antes de caer la señal. Esta
característica permite un funcionamiento más
natural del procesador, puesto que evita que en
las pausas entre los diálogos, por ejemplo, se
note la 'respiración' del AGC (incremento en el
ruido o soplido de fondo). O que al terminar un
tema musical, se escuche un aumento del ruido
de fondo antes de comenzar el tema musical
siguiente, etc.
2.2.7 SRS WOW
Expands the stereo image, obtaining a wider
stereo and surrounding sound. This stage have
incidence fundamentally on mid frequencies and
works only with stereo signals. Monoaural signals
(equal in both channels, like the voices) are not
processed.
2.2.8 MULTIBAND COMPRESSOR
The purpose of the multiband compressors is to
increase the perceived loudness sensation. The
human voice and music will sound more solid,
with better dynamic balance. Still more, the
increase of the average energy of the audio
signal is very considerable, increasing the
coverage area of the radio for A.M. and FM
transmissions (for more info please visit
www.solidynepro.com).
Multiband technology bases on the studies of
Stevens (ref 1.2.3) about the loudness of each
band frequency and the studies of Zwicker (ref
4) About its relation with the Critics Bands of the
human ear. The integration time of the ear to
reach the maximum loudness is of the order of
200 milliseconds (ref 5). This time must carefully
be incorporated to the controls of the loudness
compressors, to obtain the desired effect. The
ear will perceive a greater loudness when the
band compressors increase the relative loudness
level.
The processor Solidyne 562dsp has digital
frequency splitters with Butterworth filters of 24
dB/octave that divides the program signal in
five frequency bands: lows; low-middle; high-
middle; highs and super-highs. The sub bands
high-middle and highs works in combination with
the 5
th
band super-highs, processing the higest
frequencies of the audio spectrum. This 5
th
band is
of great importance since take incidence over the
peaks of the signal, one of the most critical
process carried out by any audio processor.
The controlling of the dynamic range using band
frequencies offers great advantages:
1.
To increase the total energy, by the use of fast
compressors for bass and ultra-fast for treble. If
the bands were not divided, the compressors
with so fast recovery time would produce a
disagreeable sound effect; the percussion of low
frequencies would modulate the high notes. And
the high notes of an instrument would as well
modulate the low tones, of a violoncello, for
example.
2.
Allows to increase the perceived loudness. This
is because most of the modulation capacity of a
transmitter or audio amplifier in general, playing
Pop music, is generally used by low frequencies
signals, below 160 Hz. Nevertheless this
information contributes very little to the loudness
sensation, due to the reduced sensitivity of the
ear for those frequencies. Therefore is desirable to
increase the level of the medium and high
frequencies. But this cannot be obtained by
simple equalizing, because the sound balance
would be destroyed. The compression in
separated bands allows to increase between 6
and 12 dB the energy for high frequencies without
altering the tone balance. In fact, the frequency
response continues being flat.
3.
Processing completely eliminate the "flat sound"
sensation, perceived when a sonorous material