SAA7715 Datasheet, PDF (20/36 Pages) NXP Semiconductors – Digital Signal Processor

Philips Semiconductors
Digital Signal Processor
Preliminary specification
SAA7715H
Table 16 Default settings of I²C-bus registers after power-up and reset
I²C-BUS ADDRESS
DEFAULT VALUE
602FH
0FFBH
0FF5H
0FF4H
0FF3H
0FF2H
0050C6H
0010DBH
000000H
000000H
000000H
000000H
9.9 Table definitions
Table 17 Digital serial format for inputs 1 to 4
FORMAT_IN 1, 2 AND 3
BIT 2
0
1
1
1
1
BIT 1
1
0
0
1
1
BIT 0
1
0
1
0
1
OUTPUT
standard I²S-bus
LSB-justified, 16 bits
LSB-justified, 18 bits
LSB-justified, 20 bits
LSB-justified, 24 bits
Table 18 Digital serial formats for outputs 1 to 4
FORMAT_OUT
BIT 2
0
1
1
1
1
BIT 1
0
0
0
1
1
BIT 0
0
0
1
0
1
OUTPUT
standard I²S-bus
LSB-justified, 16 bits
LSB-justified, 18 bits
LSB-justified, 20 bits
LSB-justified, 24 bits
10 SOFTWARE IN ROM DESCRIPTION
10.1 Audio dynamics compressor
10.1.1 THEORY OF OPERATION
The objective of a dynamics compressor is to reduce the
dynamic range of the input signal for purposes of
accommodating downstream devices, or simply to give the
audio signal a different character. Early compressors were
used primarily for limiting signals destined for recording on
media with limited dynamic range. In the present day,
compressors are routinely used in recording studios and in
live performances to enhance the presence of various
signals.
The behaviour of a dynamics compressor is very similar to
that of an Automatic Gain Control (AGC), the central idea
being to scale the input signal by a slowly varying gain
factor that is in turn regulated by the level of the input
signal. The essential concepts are summed up nicely by
Fig.7. Here we observe that when the input level exceeds
a selected threshold, gain reduction is brought to bear
according to the selected compression ratio, while signals
appearing below the threshold are passed with unity gain.
The net effect, therefore, is to compress the louder
passages of source material.
2001 May 07
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