SAA2003 データシートの表示（PDF） - Philips Electronics

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SAA2003

Stereo filter and codec

Philips Electronics 

Philips Semiconductors

Stereo filter and codec

Preliminary specification

SAA2003

PASC processor

The PASC processor is a dedicated Digital Signal

Processor (DSP) engine which efficiently codes digital

audio data at a bit rate of 384 kbits/s without affecting the

sound quality. This is achieved using an efficient adaptive

data notation and by only encoding the information which

can be heard by the human ear.

The audio data is split into 32 equal sub-bands during

encoding. For each of the sub-bands a masking threshold

is calculated. The samples from each of the sub-bands are

included in the PASC data with an accuracy that is

determined by the available bit-pool and by the difference

between the signal power and the masking threshold for

that sub-band.

The stereo filter codec performs the splitting (encoding)

and reconstruction (decoding), including the necessary

formatting functions. During encoding, the adaptive

allocation and scaling circuit calculates the required

accuracy (bit allocation) and scale factors of the sub-band

samples.

ENCODING (SEE FIG.4)

The incoming serial audio data is filtered into 32 sub-bands

for left and right (I and II) channels using the stereo filter

part of the SAA2003. A PASC frame is made up of left and

right (I and II) audio data for 12 samples from each of the

32 sub-bands, a total of 768 audio samples. For every

PASC frame the SAA2013 calculates a bit allocation and

scale factor table which is transferred to the SAA2003. All

the samples in a frame are scaled in accordance with the

scale factor calculated by the SAA2013. Once scaled the

samples are re-quantized to reduce the number of bits to

correspond with the allocation table calculated by the

SAA2013. Synchronization, allocation and scale factor

information is then added to provide a fully encoded PASC

data signal. These frames of data are then sent to the drive

processor IC (SAA2023 or SAA3323).

DECODING (SEE FIG.5)

In decoding mode the SAA2003 synchronizes and

recovers frames of data from the drive processor. The

recovered allocation data and the scale factors are used to

correctly re-quantize and re-scale the PASC sub-band

samples. The decoded sub-band samples, which are

represented in 24-bits two’s complement notation, are

reconstructed by the sub-band filters into a single

complete digital audio signal.

handbook, full pagewidth

from SAA2013

ALLOCATION AND

SCALE FACTOR

INFORMATION

TABLE

baseband

samples

SUB-BAND

FILTER

sub-band

samples

SCALING AND

QUANTI ZATION

allocation information

and scale factor indices

SYNC AND

CODING

INFORMATION

quantified samples

FORMATTER

PASC

OUTPUT

DATA

MLB764

Fig.4 Encoding mode.

May 1994

7

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