BSP3505D Micronas Intermetall GmbH, BSP3505D Datasheet - Page 19

• Manufacturer Part Number: BSP3505D
• Manufacturer: Micronas Intermetall GmbH

Micronas
PRELIMINARY DATA SHEET
4.4.14. Automatic Volume Correction (AVC)
Different sound sources fairly often do not have the
same volume level. Advertisement during movies, as
well, usually has a different (higher) volume level than
the movie itself. The Automatic Volume Correction
(AVC) solves this problem and equalizes the volume lev-
els.
The absolute value of the incoming signal is fed into a
filter with 16 ms attack time and selectable decay time.
The decay time must be adjusted as shown in the table
above. This attack/decay filter block works similar to a
peak hold function. The volume correction value with its
quasi continuous step width is calculated using the at-
tack/decay filter output.
The Automatic Volume Correction works with an internal
reference level of –18 dBFS. This means, input signals
with a volume level of –18 dBFS will not be affected by
the AVC. If the input signals vary in a range of –24 dB to
0 dB, the AVC compensates this.
Example: A static input signal of 1 kHz on Scart has an
output level as shown in the table below.
AVC
AVC
AVC
AVC
8 sec (long)
4 sec (middle)
2 sec (short)
20 ms (very short)
Scart Input
0 dbr = 2 Vrms
0 dBr
–6 dBr
–12 dBr
–18 dBr
–24 dBr
–30 dBr
Loudspeaker Volume = 73
Scart Prescale = 20
on/off
off and Reset
of int. variables
on
Decay Time
Volume
Correc-
tion
–18 dB
–12 dB
–6 dB
–0 dB
+ 6 dB
+ 6 dB
hex
i.e. 2.0 Vrms = 0 dBFS
hex
0029
0000
RESET
1000
0029
1000
0100
0010
0001
= 0 dBFS
hex
hex
Main Output
0 dBr = 1.4 Vrms
–18 dBr
–18 dBr
–18 dBr
–18 dBr
–18 dBr
–24 dBr
[15.12]
0
8
[11..8]
8
4
2
1
hex
hex
hex
hex
hex
hex
To reset the internal variables, the AVC should be
switched off and on during any channel or source
change. For standard applications, the recommended
decay time is 4 sec.
Note: AVC should not be used in any Dolby Prologic
mode, except PANORAMA, where no other than the
loudspeaker output is active.
4.5. DSP Read Registers: Functions and Values
All readable registers are 16-bit wide. Transmissions via
I
entries are 8 bit. Some of the defined 16-bit words are
divided into low and high byte, thus holding two different
control entities.
These registers are not writeable.
4.5.1. Quasi-Peak Detector
The quasi peak readout register can be used to read out
the quasi peak level of any input source, in order to ad-
just all inputs to the same normal listening level. The re-
fresh rate is 32 kHz. The feature is based on a filter time
constant:
attack-time: 1.3 ms
decay-time: 37 ms
2
C bus have to take place in 16-bit words. Single data
Quasi-Peak
Readout Left
Quasi-Peak
Readout Right
Quasi peak readout
0019
001A
[0
values are 16 bit two’s
complement
hex
BSP 3505D
hex
hex
... 7FFF
hex
H+L
H+L
]
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