11-26
Audio Decoder Module
If the data in the Linear PCM bitstream does not agree with the options
available, the decoder sets the Context Error Interrupt bit in Register 4
(page 4-9), asserts INTRn to the host if the interrupt is not masked,
mutes the audio output, and searches for the next sync word.
Dynamic Range Control is a compressed gain value that should be
applied to all the samples in an audio frame. One audio frame has 80 or
160 samples when the sampling frequency is 48 or 96 kHz, respectively.
One audio frame can extend across an audio pack boundary. The rst
byte location of an audio frame is dened by the rst access pointer. All
Linear PCM samples in one audio frame have a unique dynamic range
control gain value, even if the audio frame is separated by an audio pack
boundary. The host can turn Dynamic Range Control on or off by setting
or clearing the Dynamic Range On bit in Register 364
(page 4-113).When the Dynamic Range Control is off, the default gain value is one.
When Dynamic Range Control is on, the decoder uses the dynamic
range control value (dynrange_value) included in the bitstream for each
audio frame. The host can also specify dynscale values in Registers 360
and 361 (
page 4-111) to scale the bitstream dynrange_value. The
dynscale factors are in increments of 1/256.
The host can also program a direct scale factor into the PCM Scale [7:0]
bits in Register 362
(page 4-111). Settings here are also in 1/256
increments. The nal sample value is computed using the following
equation:
nal sample value = [|dynrange_value - 1|* dynscale(high/low) + 1]
*PCM Scale * decoded sample
The Linear PCM Decoder produces stereo PCM and S/P DIF outputs.
Up to two channels of Linear PCM samples can be decoded; additional
channel samples are dropped. When the Linear PCM bitstream contains
only one channel, PCM and S/P DIF output samples in the rst channel
are duplicated in the second channel.
11.6.3 Other Host Controls and Status
The bitstream mute, emphasis, quantization, and sampling frequency
information is written to Register 352
(page 4-103) for the host. The
audio_frm_num and num_of_audio_ch are written to Register 351. When
the mute bit in the audio packet is 1, PCM samples are muted by the
output DAC and S/P DIF interface.