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24.4. Digital Signal Processing (DSP) Stage
24.4.1.Dolby Pro Logic Processing
As already mentioned the DPL3519A
IC2401
also
performs Dolby Pro Logic processing. To do this the
left and right audio signals are fed to the Surround
Source Select circuit.
The Surround Source Select circuit is used to switch
between the input audio signals and the noise signal
fed from the noise generator, which is used to help the
user set-up the volume levels of the Left/Right/Centre
and Surround channels and is discussed later
The selected audio signal is then fed to the following
Surround Source Matrix which is used to select the
signal type (Stereo, Mono, L only, R only signals). To
enable the Decoder to produce a Dolby Pro Logic
output either Active or Passive then a stereo signal is
required.
24.4.2.Surround Decoder
The processing performed by the Surround Decoder
previously described in section 23.2.
is responsible for reproducing a Dolby Pro Logic
Active or Passive signal, as well as providing a
number of sound effects which are normally used
when processing a mono signal.
When Dolby Pro Logic Active mode (Normal Mode)
is selected the left (L) / centre (C) / right (R) and
surround (S) signals are output from the Surround
Decoder in signal pairs (L and R, C and S) to the
Channel Source Select switch. Here the L/R and
C/S signals are fed via the output channel paths
which sees the signals being output from the
following output terminals:
:
Left output via the I2S bus
:
Right output via the I2S bus
:
Centre output pin 25
:
Surround output pin 24
Also provided on some models is an additional
channel called Super 3D Bass, which is used to
provide additional bass, producing more depth and
impact. A good example of this being a scene with
explosions where the Super 3D Bass makes them
more dramatic. This Super 3D Bass being output via
the following terminal:
:
Super 3D Bass output pin 27
Where Dolby Pro Logic Passive mode (Phantom
mode) is selected there is no centre channel output.
Instead this signal is divided and added between the
front left and right channels.
Summary of Contents for EURO 4 Chassis
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