LM49352 datasheet(75/106 Pages) TI

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Audio

Compressor

Output Level

(dB)

Audio Compressor Input

Level

(dB)

Audio

Compressor

Threshold

Level

1:2 Compression

Ratio

1:215

Compression

Ratio

1:4 Compression

Ratio

1:1 Compression

Ratio

LM49352

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SNAS467E – MARCH 2009 – REVISED MARCH 2013

Digital Audio Compressor

The LM49352 features a digital audio compressor on both the DAC and ADC paths. The compressor works by

reducing the level of the audio signal that is higher than the level set by the audio compressor threshold level

(THRESHOLD) by a fixed ratio (compressor output / compressor input) that is set by a predetermined audio

compression ratio (RATIO). Higher compression ratios result in more compression as shown in Figure 70. The

audio compressor can be used in conjunction with the ALC to limit audio peaks that the ALC may not be fast

enough to react to.

Figure 70. Audio Compressor Effect

Soft Knee Function

The LM49352’s audio compressor also features a soft knee function that smooths the harsh edges found during

clipping of an audio signal. For audio signals higher than the compressor threshold level, the soft knee function

gradually increases the compression ratio for increasing levels of audio signal beyond the compressor threshold.

To achieve the smoothing effect to prevent hard clipping, the soft knee function initially compresses the audio

signal at the smallest ratio and then incrementally increases the compression ratio if required. The highest level

of compression applied by the soft knee function is set by the compressor ratio. The effect of the soft knee

function is shown in Figure 71.

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