SRC4382IPFBT datasheet(36/81 Pages) BURR-BROWN

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SRC4382

SBFS030B – JANUARY 2006 – REVISED APRIL 2006

PRODUCT OVERVIEW (continued)

DEM0 and DEM1 bits. The AUTODEM function automatically enables and disables the de-emphasis filter for the

required sampling rate based upon the setting of the pre-emphasis and sampling frequency channel status bits

in the AES3 or S/PDIF input data stream, which are decoded by the DIR block. The AUTODEM feature functions

only when both 50/15

µs pre-emphasis and one of the three supported sampling rates (32kHz, 44.1kHz, or

48kHz) are decoded by the DIR. By default, the de-emphasis filter, including the AUTODEM function, is

disabled.

The group delay of the SRC interpolation function can be programmed to one of four settings. The actual length

of the interpolation filter is unaltered, but the number of samples pre-buffered in the FIFO prior to the re-sampler

function can be set to 64, 32, 16, or 8. The FIFO length directly impacts the latency and group delay. By default,

the number of samples pre-buffered is set to 64.

The decimation filter includes a direct down-sampling option. This option should only be used in cases where the

output sampling rate is higher than the input sampling rate. The advantage of using the direct down-sampling

option is that it results in zero latency operation, as it simply selects one out of every 16 samples from the

re-sampler output without applying low-pass anti-aliasing filtering. By contrast, the decimation filter response

adds 36.46875 samples of group delay. The disadvantage of the direct down-sampling option is that it cannot be

used in cases where the output sampling rate is equal to or lower than the input sampling rate, since the lack of

low-pass filtering results in aliasing. By default, the decimation filter is enabled, as the initial values of the input

and output sampling rates may be unknown.

The SRC includes two status registers that contain the integer and fractional parts of the input-to-output

sampling ratio, which is derived by the SRC rate estimator circuitry. These registers can be read back any time

the RDY output is low. When either the input or output sampling rate is known, the unknown sampling rate can

be calculated using the contents of these status registers.

The SRC provides a simple word length reduction mechanism for reducing 24-bit audio data to 20-, 18-, or 16-bit

output word lengths. Word length reduction is performed utilizing triangular probability density function (or TPDF)

dither. The OWL0 and OWL1 bits in control register 0x2F are utilized to set the SRC output word length.

One note concerning the SRC output word length setting: when using the SRC output as the data source for

either the Port A or Port B serial data outputs, and the audio serial port data format is set to Right-Justified, the

word length set for the audio serial port format must match the word length set for the SRC output data.

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SRC4382IPFBT Datasheet(PDF) 36 Page - Burr-Brown (TI)