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SOLIDYNE 462
dsp - broadcast digital processor Page 31
2.2.8 LOW PASS 15 KHz DIGITAL FILTER
In order to be in agreement with the standards for
FM stereo transmission, a 15KHz low-pass filter is
at the input of the stereo coder, which produces
an attenuation > 50 dB at 16.6 KHz; to avoid
interference with the RDS sub-carrier; and > 60 at
the pilot tone (19 KHz).
Is an digital elliptical filter; of great stability. This
filter also guarantees that not exist spurious
components at the RDS band of 57 KHz.
2.2.9 DIGITAL STEREO CODER
It uses digital technology to generate the MPX
signal. This technique, created by
Solidyne, allows obtaining a coder with excellent
features; 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 that take place at 53 KHz,
which no allow to achieve a good channel
separation. 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 7).
2.2.10 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, called 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.
Solidyne processors 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 in the audio band.
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