TAS5504 datasheet(34/96 Pages) TI

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Introduction

SLES123 − October 2004

TAS5504

O1No Discontinuity + |T1 * T2| k1 ) O2 For ( |T1| w |T2| )

T1 and T2 are the threshold settings in dB, k1 is the slope for region 1, and O2 is the offset in dB at T2. If the

user chooses to select a value of O1 that does not obey the above equation, a discontinuity at T1 is realized.

Going down in volume from T2, the slope k1 remains in effect until the input level T1 is reached. If, at this input

level, the offset of the transfer function curve from the 1:1 transfer curve does not equal O1, there is a

discontinuity at this input level as the transfer function is snapped to the offset called for by O1. If no

discontinuity is wanted, O1 and/or k1 must be adjusted so that the value of the transfer curve at the input level

T1 is offset from the 1:1 transfer curve by the value O1. The examples that follow illustrate both continuous

and discontinuous transfer curves at T1.

Going down in volume from T1, starting at the offset level O1, the slope k0 defines the compression/expansion

activity in the lower region of the DRC transfer curve.

1.10.2.1 Threshold Parameter Computation

For thresholds,

TdB = −6.0206TINPUT = −6.0206TSUB_ADDRESS_ENTRY

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

is:

T1SUB_ADDRESS_ENTRY +

*64

*6.0206 +

10.63

T1 is entered as a 48-bit number in 25.23 format. Therefore:

T1 = 10.63 = 0_1010.1010_0001_0100_0111_1010_111

= 0x00000550A3D7 in 25.23 format

1.10.2.2 Offset Parameter Computation

The offsets set the boost or cut applied by the DRC-derived gain coefficient at the threshold point. An

equivalent statement is that offsets represent the departure of the actual transfer function from a 1:1 transfer

at the threshold point. Offsets are 25.23 formatted 48-bit logarithmic numbers. They are computed by the

following equation.

OINPUT +

ODESIRED ) 24.0824 dB

6.0206

Gains or boosts are represented as negative numbers; cuts or attenuation are represented as positive

numbers. For example, to achieve a boost of 21 dB at threshold T1, the I2C coefficient value entered for O1

must be:

O1INPUT +

–21 dB ) 24.0824 dB

6.0206

+ 0.51197555

+ 0.1000_0011_0001_1101_0100

+ 0x00000041886A in 25.23 format

More examples of offset computations are included in the following examples.

TAS5504 Datasheet(PDF) 34 Page - Texas Instruments

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