TAS5705PAPR datasheet(37/71 Pages) TI

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SUB_ADDRESS_ENTRY

Τ1

= 10.63

6.0206

k =

(1)

Compression equation: k =

4 =

n =

0.3333:1 compression

® -

(g /20)

offset

15.5

TAS5705

www.ti.com ...................................................................................................................................................................................................... SLOS549 – JUNE 2008

Threshold Parameter Computation

For thresholds,

Tdb = –6.0206 TINPUT = –6.0206 TSUB_ADDRESS_ENTRY

If, for example, it is desired to set T1 = –64 dB, then the subaddress entry required to set T1 to –64 dB is

T1 is entered as a 32-bit number in 9.23 format. Therefore,

T1 = 10.63 = 0 1010.1010 0001 0100 0111 1010 111 = 0x0550 A3D7 in 9.23 format

Slope Parameter Computation

In developing the equations used to determine the subaddress input value required to realize a given

compression or expansion within a given region of the DRC, the following convention has been adopted.

DRC Transfer = Input Increase : Output Increase

If the DRC realizes an output increase of n dB for every dB increase in the rms value of the audio into the DRC,

a 1:n expansion is being performed. If the DRC realizes a 1-dB increase in output level for every n dB increase in

the rms value of the audio into the DRC, an n:1 compression is being performed.

For a 1:n expansion, the slope k can be found by

k = n – 1

For an n:1 compression, the slope k can be found by

In compression (n:1), n is implied to be greater than 1. For compression, Equation 1 means –1 < k < 0 for n > 1.

Thus k must always lie in the range k > –1.

With k = –4 then, the output decreases 3 dB for every 1-dB increase in the rms value of the audio into the DRC.

As the input increases in signal amplitude, the output decreases in signal amplitude.

DRC Offset Calculation

The DRC offset is calculated by

where gd = desired gain (in dB) and 15.5 is the the fixed antilog normalization factor. A value of gd = 0 indicates

no offset.

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