DA7219 Datasheet, PDF (29/123 Pages) Dialog Semiconductor – Audio codec with Advanced Accessory Detect

DA7219
Audio codec with Advanced Accessory Detect
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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, as 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 clipping function that applies a very fast attack
rate when the input signal is close to full-range. 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 threshold above which it is activated 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.
input signal
gain level
atk rate
dcy rate
max
min
time
atk
hld
dcy
time
Figure 11: Attack, delay and hold parameters
9.3.2 Sidetone processing
There is a low latency filter channel between inputs and outputs for implementing a sidetone path.
The gain is controlled using sidetone_gain and provides gain in the range -42 dB to +0 dB in +3 dB
steps.
The sidetone path is enabled using sidetone_en. It is muted using sidetone_mute_en.
The output from the sidetone channel can be added to left or right (or both) output filters using
outfilt_st_1l_src and outfilt_st_1r_src.
The sidetone path is enabled using sidetone_en. It is muted using sidetone_mute_en.
Datasheet
Revision 2.1
29 of 123
17-Dec -2015
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