AK4635 datasheet(45/81 Pages) AKM

45 / 81 page

[AK4635]

Rev. 0.6

2007/10

- 45 -

■ ALC Operation

ALC Operation works in ALC block. When ADCPF bit = “1”, ALC operation is enable for recording path. When ADCPF

bit = “0”, ALC operation is enable for playback path. The ON/OFF of ALC operation for recording is controlled by ALC1

bit and the ON/OFF of ALC operation for playback is controlled by ALC2 bit.

1. ALC Limiter Operation

When the ALC limiter is enabled, and output exceeds the ALC limiter detection level (Table 25), the volume value is

attenuated by the amount defined in LMAT1-0 bits (Table 26) automatically.

When the ZELMN bit = “0” (zero crossing detection valid), the VOL value is changed by ALC limiter operation at the

zero crossing point or zero crossing timeout. Zero crossing timeout period is set by ZTM1-0 bit that in common with ALC

recovery zero crossing timeout period’s setting (Table 27).At LFST bit = “1”, VOL value is attenuated 1step immediately

(period : 1/fs) when output Level is over FS(Digital Full Scale).

When the ZELMN bit = “1” (zero crossing detection invalid), VOL value has been changed immediately (period: 1/fs) by

ALC limiter operation. The attenuation for limiter operation is fixed to 1 step and not controlled by setting LMAT1-0 bits.

After finishing the attenuation operation, if ALC bit does not change to “0”, the operation repeats when the output signal

level exceeds the ALC limiter detection level.

LMTH1

LMTH0 ALC Limiter Detection Level

ALC Recovery Waiting Counter Reset Level

ALC Output

≥ −2.5dBFS

−2.5dBFS > ALC Output ≥ −4.1dBFS

ALC Output

≥ −4.1dBFS

−4.1dBFS > ALC Output ≥ −6.0dBFS

(default)

ALC Output

≥ −6.0dBFS

−6.0dBFS > ALC Output ≥ −8.5dBFS

ALC Output

≥ −8.5dBFS

−8.5dBFS > ALC Output ≥ −12dBFS

Table 25. ALC Limiter Detection Level / Recovery Waiting Counter Reset Level

ALC1 Limiter ATT Step

LMAT1

LMAT0

ALC1 Output

≥ LMTH

ALC1 Output

≥ FS

ALC1 Output

≥ FS + 6dB

ALC1 Output

≥ FS + 12dB

(default)

Table 26. ALC Limiter ATT Step Setting

Zero Crossing Timeout Period

ZTM1

ZTM0

8kHz

16kHz

44.1kHz

128/fs

16ms

8ms

2.9ms

(default)

256/fs

32ms

16ms

5.8ms

512/fs

64ms

32ms

11.6ms

1024/fs

128ms

64ms

23.2ms

Table 27. ALC Zero Crossing Timeout Period Setting

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