TLV320AIC27

STEREO AUDIO CODEC

SLAS253A – MARCH 2000 – REVISED SEPTEMBER 2000

10

POST OFFICE BOX 655303

3D stereo enhancement (continued)

There is no provision for pseudo-stereo effects. Mono signals have no enhancement applied if they are in phase

and have the same amplitude.

Signals from the PCM DAC channels do not have stereo enhancement applied. It is assumed that these signals

have already been processed digitally with any required 3D-enhancement effect. Applying the analog

3D-enhancement will corrupt the digital effect. This is equivalent to setting the POP bit in register 20h. As a

result, the readback value of this bit is fixed as 1, and attempts to change it will be ignored. The POP bit is set

to one and cannot be reset.

variable sample rate support

The DACs and ADCs on this device support all the recommended sample rates specified in the Intel Revision

2.1 specification for both audio and modem rates. Default rates are 48 ksps. If alternative rates are selected,

the AC’97 interface continues to run at 48 kw/s (kilowords per second), but data is transferred across the link

in bursts such that the net sample rate selected is achieved. It is up to the AC’97 Revision 2.1-compliant

controller to ensure that data is supplied to the ac link, and received from the ac link at the appropriate rate.

The device supports on-demand sampling. That is, when the DAC signal-processing circuits need another

sample a request is sent to the controller, which must respond with a data sample in the next frame it sends.

For example, if a rate of 24 ksps is selected, on average the device requests a sample from the controller every

other frame, for each of the stereo DACs. Note that if an unsupported rate is written to one of the rate registers,

the rate defaults to the nearest rate supported. The register then responds when interrogated with the supported

rate the device has defaulted to.

ADCs are controlled similarly but with one difference: normally the left and right-channel ADCs sample at the

same rate.

Table 1. Variable Sample Rates Supported

AUDIO

SAMPLE RATE

CONTROL VALUE

D15–D0

MODEM

SAMPLE RATE

CONTROL VALUE

D15–D0

8000

1F40

7200

1C20

11025

2B11

8228.57 (57600/7)

2024

16000

3E80

8400

20D0

22050

5622

9000

2328

44100

AC44

9600

2580

48000

BB80

10285.71 (72000/7)

282D

12000

2EE0

13714.28 (96000/7)

3592

19200

4B00

24000

5DC0