DA7217 datasheet(36/171 Pages) DIALOG

36 / 171 page

DA7217

Ultra-Low Power Stereo Codec

Datasheet

Revision 2.5

01 Sep 2016

CFR0011-120-00

36 of 171

Similarly the minimum and maximum levels of analog gain are controlled by alc_ana_gain_min and

alc_ana_gain_max. The rates at which the gain is changed are defined by the attack and decay rates

in register ALC_CTRL2. When attacking, the gain decreases with alc_attack rate. When decaying,

the gain increases with alc_release rate.

Hybrid mode should be used whenever analog microphones are being used. Digital-Only mode

should be used whenever digital microphones are being used.

The hold-time is defined by alc_hold in the ALC_CTRL3 register. This controls the length of time that

the system maintains the current gain level before starting to decay. This prevents unwanted

changes in the recording level when there is a short-

lived ‘spike’ in input volume, for example when

recording speech.

Typically the attack rate should be much faster than the decay rate. To avoid clipping it is necessary

to reduce rapidly increasing waveforms as quickly as possible, whereas fast release times will result

in the signal appearing to ‘pump’. The ALC also has an anti-clip function that applies a very fast

attack rate when the input signal is close to full-scale. This prevents clipping of the signal by reducing

the signal gain at a faster rate than would normally be applied. The anti-clip function is enabled using

alc_anticlip_en, and the trigger threshold is set in the range 0.034 dB/FS to 0.272 dB/FS using

alc_anticlip_step.

A recording noise-gate feature is provided to avoid increasing the gain of the channel when there is

no signal, or when only a noise signal is present. Boosting a signal on which only noise is present is

known as ‘noise pumping’, the noise-gate prevents this. Whenever the level of the input signal drops

below the noise threshold configured in alc_noise, the channel gain remains constant.

Figure 12: Attack, Delay and Hold Parameters

9.3.1.4

Input Dynamic Range Extension

When using analog microphones, the input dynamic range extension (DRE) automatically swaps the

analog and digital gains to maximize the dynamic range at all times.

max

min

atk

dcy

hld

input signal

gain level

atk rate

dcy rate

time

DA7217 Datasheet(PDF) 36 Page - Dialog Semiconductor

DA7217 Datasheet(HTML) 36 Page - Dialog Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL