AUDIMAX 362 HD, Owner'S Manual

Page: 17 / 19

Stage 6: Energy Bands
Band Energy controls increase the peak density of
the audio bands, obtaining signals with very high
loudness. Knobs act on the recovery times of the
compressors. Each band have a different recovery
time, of variable range.
"Energy Bands" adjusts according to the music’s
style that the radio manages. Turning the controls to
the left you will have a smooth sound (long recovery
times); whereas turning them to the right you
increases the energy for the bands, which will
produce a more “hard" sound with great "punch"
and "sharp" highs (fast recovery times). As example
we say that for melodic music, classic (academic),
etc., in which there is no noticeable rhythmical
support, agrees not to emphasize too much the
Energy Band controls, that is to say, to use long
recovery times. For Rock & Pop is advisable to
increase the energy bands so that the sound has
more "punch".
Stage 7: Stereo Coder
The sum of the signals is sent to the stereo coder .
It uses digital technology to generate the MPX
signal. This technique, created by Solidyne, allows
to obtain a perfect coder with distortion 10 times
below the audibility threshold and channel
separation better than 75 dB.
It’s based on the oversampling concept, that divides
the audio signal in 16 samples that are processed
separately at 38 x 16 = 608 KHz. Due to this
elevated sampling rate, the anti-alias filters works
over 500 KHz, eliminating the “phase rotation” effect
at 53 KHz. With this new solution and the use of
advanced technology in each part of the circuit,
residual components of distortion below -90 dB are
obtained.
It is described separately in this manual, the way to
do measurements and reception tests of the stereo
coder (see Chapter 4).
MPX processing
The studies about the modulation on an FM
transmitter indicate that when the transmitter is
modulated by stereo MPX signal appears a new
effect, not present on the original audio signal.
This effect, denominated in U.S.A. MPX
Interleaving (also known as peak correlation ),
determines that the modulation peak in MPX does
not coincide with the modulation peak of the stereo
signal, considered in independent form.
This means, in simple terms, that if the peaks of
channels L and R are limited separately so that
MPX signal never over modulate, during most of the
time, the modulation capacity of the transmitter will
be wasted. And this happens because signal MPX
is the sum of L+R but also includes the 38 KHz sub-
carrier. According to the relation of phase between
these three elements, there will be different peak
values for the interleaving. This phenomenon
indicates that is possible to increase the modulation
without increasing the deviation of 75 KHz of the
transmission, taking advantage of the modulation
capacity that normally is wasted.
Audimax 362HD processor uses a MPX Processing
technology named Super Modulation. This
processing consists on a system that controls the
peaks, operating at 608 Khz, eliminating the peaks
in MPX base band signal and filtering them so that
there are not left residual components.
REFERENCES
1.- S. S. Stevens, The measurement of loudness, ASA Journal, Vol.27,
pg. 815.
2.- S. S. Stevens, The direct estimations of sensory magnitudes-
loudness; American J. Psychol. 69, 1-25, 1956.
3.- S. S. Stevens, Concerning the form of the loudness function; ASA
Journal, Vol. 29, pg 603-606, 1957.
4.- E. Zwicker – Flottrop – Stevens; critical bandwidth in loudness
sumation, ASA Journal, Vol. 29, pg. 548-557, 1957.
5.- Stanley Gelfand, Hearing, pg. 392, Edited by M. Dekker, N. York,
1990.
6.- Oscar Bonello. NEW IMPROVEMENTS IN AUDIO SIGNAL
PROCESSING Journal of the Audio Engineering Society, Vol. 24 Nº
5. USA, 1976
7.- Oscar Bonello PC CONTROLLED PSYCHOACOUSTIC AUDIO
PROCESSOR, 94th Audio Convention, Berlin March 1993
8.- Oscar Bonello, Burst Masking (Enmascaramiento por Ráfaga)
Anales del II Congreso Iberoamericano de Acústica, Madrid,
octubre 2000
9.- Oscar Bonello, Multiband Audio Processing and Its Influence on the
Coverage Area of FM Stereo Transmission, Journal of Audio
Engineering Society, New York, March 2007
SOLIDYNE Audimax 362HD Page 17