cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 128

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

Detailed Functional Description
3.25.4
3.25.5
Figure 3-40. Shelving Filters Used for Boosting or Cutting Treble or Base
3-102
Gain
1
Lowpass Shelving Filter Frequency
Soft Mute
Tone Controls
Frequency
Response (Magnitude)
Cutoff
Boost
Cut
Pathway
In addition to individual volume control, the baseband processing provides a soft mute
command that individually mutes each of the three channels in about 40 ms with a
smooth transition. The advantage of the mute command over the volume control is
that the un-mute command restores the previous volume setting with no need for the
external control microprocessor to read and resend the original setting. It also
eliminates popping sounds when changing between mute and un-mute.
If an immediate mute or un-mute command is needed, the processor can provide an
immediate mute or un-mute function that eliminates the delay for muting. This
produces an audible click, but is useful in some situations.
The soft mute function and the determination of what source to mute is configured by
the registers defined by pathway:
A three-band equalizer is integrated into the device to be used for boosting or
attenuating the various bands of the audio spectrum with a range of +12 dB. The
simplest implementation is a three-band equalizer where the bass (low frequencies),
mid-tone, and treble (high frequencies) can all be separately adjusted. This is
accomplished by using a low-pass shelving filter, mid-range peaking filter, and high-
pass shelving filter. These filters are illustrated in
Path 1
Path 2
Frequency
Conexant
Variable
Mute
Mute
Gain
1
Highpass Shelving Filter Frequency
Response (Magnitude)
Figures 3-40
Register
0x8D3
0x8E3
Boost
Cut
Frequency
Cutoff
and 3-41.
CX25840/1/2/3 Data Sheet
Frequency
102284B
102284_043
8/3/05