ST18AU1_DS データシートの表示（PDF） - STMicroelectronics

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ST18AU1_DS

SIX-CHANNEL DOLBY AC3/MPEG2 AUDIO DECODER

STMicroelectronics 

ST18-AU1

1 INTRODUCTION

The ST18-AU1 is a single-chip multi-function audio processor for Dolby AC-3, MPEG-1/

MPEG-2 Layer-I/II audio encoded bitstreams, and DVD Linear PCM. It is capable of decoding

up to 5.1 channels of input Dolby AC-3 or MPEG-2 multi-channel encoded audio, and down

mixing to 2 channels of PCM output audio. Maximum input data rates for Dolby AC-3 bitstream

and MPEG-2 audio bitstream are 448 Kbits/s and 912 Kbits/s respectively. It also supports up

to 8 channel linear PCM input with by-pass, down-sampling, and down-mixing function. The

linear PCM multi-channel input modes available are:

• 48 kHz/16-bit up to 8 ch @ max 6.144 Mbps

• 48 kHz/20-bit up to 6ch @ max 5.760 Mbps

• 48 kHz/24-bit up to 5ch @ max 5.760 Mbps

• 96 kHz/16-bit up to 4ch @ max 6.144 Mbps

• 96 kHz/20-bit up to 3ch @ max 5.760 Mbps

• 96 kHz/24-bit up to 2ch @ max 4.608 Mbps

• 44.1 kHz/16-bit 2ch (CD-DA).

The input bitstream is taken from the multi-format serial input, and decoded according to the

selected MPEG-1, MPEG-2 (in the case of Karaoke capable mode), AC-3 decoder or Linear

PCM processor. A Packet Demux de-multiplexes the input if it is MPEG-1 or DVD/MPEG-2

PES packetized. For an input bitstream with more than 2 encoded audio channels, the

decoded channels are mixed down to 2 channels with the Dolby Surround compatible or

karaoke capable option, and outputted through a multi-format serial output port. The input AC-

3, MPEG bitstream, or decoded PCM can be outputted through an IEC-958 (S/PDIF)

Formatter/Transmitter. The AC-3 or MPEG S/PDIF output bitstream is delayed and

synchronized with the output decoded PCM.

The Karaoke Capable mode defined in Dolby AC-3 or DVD to allow the multi-channel audio

stream to convey channels designed as L, R (2-ch stereo music), M (guide melody), and V1,

V2 (one or two vocal/supplementary tracks) are supported. This Karaoke capable decoder

allows the user to choose to have the decoder reproduce any of the guide melody and vocal/

supplementary channels. Centre and surround mix levels either controlled by the user or within

the bitstream are used to down mix the M channel and the V1, V2 channels respectively.

The selectable Linear PCM Processor functions are:

• down-mixing to 2 channels,

• down-sampling for 96kHz to 48kHz,

• noise shaped quantization for 24-bits or 20-bits to 16-bits.

Depending on the application, the decoded PCM audio output is selectable to be 16, 18, 20 or

24 bits, and the sampling rates of the PCM output are 32 kHz, 44.1 kHz, 48 kHz or 96 kHz.

External A/V synchronization can be assisted by the System Time Clock (STC) within the

Timer and the PTS extracted from the packetized input. A serial I2C interface to host

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