SAA2501 Datasheet, PDF (12/52 Pages) NXP Semiconductors – Digital Audio Broadcast DAB decoder

Philips Semiconductors
Digital Audio Broadcast (DAB) decoder
Preliminary specification
SAA2501
When using the master input with FSCLKM = 0, the
SAA2501 selects the active sample rate autonomously,
and generates the signals SCK and WS from its crystal
clocks. After a device reset, the SAA2501 selects a sample
rate of 44.1 kHz by default.
SCK and WS may, and will only, show phase or frequency
changes in any of the following 3 situations:
1. When the SAA2501 establishes synchronization with
the coded data input bitstream.
2. When the active input interface is changed from the
master input with FSCLKM = 0 to the slave input (i.e.
the timing source for the generation of SCK and WS is
switched from the crystal clocks to FSCLKIN).
3. When the active input interface is changed from the
slave input to the master input with FSCLKM = 0 (i.e.
the timing source for the generation of SCK and WS is
switched from FSCLKIN to the crystal clocks); the
sample rate is set to the last selected sample rate that
was used with the master input (the last selected
sample rate is memorized while using the slave input).
In all other cases, SCK and WS keep on running without
phase or frequency changes, and the sample rate
selection remains unchanged.
7.13 Handling of errors in the coded input data
The SAA2501 can handle errors in the input data. Errors
are assumed to be present in 3 events:
1. If errors are indicated with the coded input data error
flag CDSEF and/or CDMEF.
2. On CRC failure if ISO/MPEG error protection is active.
3. If input bitstream syntax errors are detected.
Errors in the input data have an effect on the decoding
process if the corrupted data is inside the header, bit
allocation or scale factor select information field in a frame
(then the SAA2501 will mute) or inside the scale factor field
(then the previous scale factor will be copied). Errors in
other data fields are not handled explicitly. If the
ISO/MPEG CRC is active, only the CRC result is
interpreted: CDSEF/CDMEF un-reliability indications for
bit allocation and scale factor select information are
neglected.
In applications where the ISO/MPEG CRC is always
present, the protection bit (which itself is not protected) in
the ISO/MPEG header may be overruled by making L3
settings flag CRCACT HIGH. In this manner, the SAA2501
is made robust for data errors on the protection bit.
7.14 Sub-band filter signals
The decoded sub-band signals are output, together with
an error indication so that concealment can be applied
externally. The optionally concealed sub-band signals are
put back into the SAA2501 for synthesis filtering.
7.15 Baseband audio processing
The baseband audio de-emphasis as indicated in the
ISO/MPEG input data is performed digitally inside the
SAA2501. The incorporated ‘Audio Processing Unit’ (APU)
(see Fig.5) can be used to apply inter-channel crosstalk or
independent volume control per channel. The APU
attenuation coefficients LL, LR, RL and RR may be
changed dynamically by the host microcontroller, writing
their 8-bit indices to the SAA2501 over the L3 control bus.
The coefficient changes become effective within one
sample period after the coefficient index writing.
To avoid clicks at coefficient changes, the transition from
the current attenuation to the next is smoothed. The
relation between the APU coefficient index and the actual
coefficient (i.e. the gain) is given in Table 5.
January 1995
12