TAS5548DCAR datasheet(43/116 Pages) TI1

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Compression equation: k

–4

–0.3333 : 1 compression

Expansion equation: k

–4

1 : –3 expansion

–

→

= –

→

–

= –

→

TAS5548

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SLES270A – NOVEMBER 2012 – REVISED APRIL 2015

As can be seen, the same value for k is obtained either way. The ability to choose values of k less than –1

allows the DRC to implement negative-slope transfer curves within a given region. Negative-slope transfer curves

are usually not associated with compression and expansion operations, but the definition of these operations can

be expanded to include negative-slope transfer functions. For example, if k = –4

With k = –4, 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 volume, the output decreases in volume.

7.4.17 THD Manager

The THD manager is designed to set the max output level target after all processing has been completed. The

Audio clip engages at +24dB between (pre) and (post) stage. 10% distortion occurs when audio is clipping

approx +2.4 to 3dB over full scale. There is amplitude loss when clipping, so THD(post) might allow slight gain

through THD manager. 10% distortion clipping will account for approx -1dB of output level loss. This is accounted

for as seen with +1dB in step 2 to set output level +0dB

Example setup to modify 10% THD output level: * note that coefficient calculations are approximate for simplicity

1. Signal path settings

–

Input -10dBFS

–

Volume 0xD9 0000 000C +15dB

–

THD Manager (pre) 0xE9 0650 0000 +22dB

–

THD Manager (post) 0xEA 0006 7000 -26dB

2. resulting output

–

output clipping at 10% distortion with output level +0dB

–

input -10 vol +15 THD(pre) +22 THD(post) -26

–

-10 +5 +27(clip) +1

3. Begin clipping at -12dBFS input with +0dB output level

–

THD Manager (pre) 0xE9 07FF FFFF +24dB (previous setting +22dB + 2dB)

–

result: input -12dBFS output clipping at 10% distortion with output level +0dB

–

input -12 vol +15 THD(pre) +24 THD(post) -26

–

-12 +3 +27(clip) +1

4. Begin clipping at -12dBFS input with -10dB output

–

THD Manager (post) 0xEA 0002 0000 -36dB (previous setting -26dB -10dB)

–

result: input -12dBFS output clipping at 10% distortion with output level +0dB

–

input -12 vol +15 THD(pre) +24 THD(post) -36

–

-12 +3 +27(clip) -9

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