TFA9879 NXP Semiconductors, TFA9879 Datasheet - Page 19

• Manufacturer Part Number: TFA9879
• Description: The TFA9879 contains a processor that supports a range of sound processing featuresincluding a 5-band parametric equalizer, separate bass and treble control, a dynamicrange compressor, soft clip control and volume control
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TFA9879
Product data sheet
9.2.10.1 Functional description
9.2.10.2 DRC control
The DRC compresses the dynamic range of the audio stream. The volume control,
equalizer or bass/treble controls can be set so that the audio stream exceeds the 0 dBFs
clip level. The DRC can be programmed to compress the louder audio content when this
occurs, while quieter sounds remain unaffected, i.e. the DRC soft clips the audio stream.
This is useful when background noise overpowers quiet audio passages. Increasing the
volume using the volume control can make quiet audio passages audible but can cause
louder audio passages to be distorted by clipping. The DRC prevents this distortion
happening by reducing the volume during loud audio passages and increasing it again for
quiet passages.
The design of the DRC feedback loop, incorporating the equalizer and bass and treble
controls, is illustrated in
The DRC has four programmable control settings:
The DRC reduces the volume when the audio signal level exceeds the attack level. The
attack level is based on the audio peak value. When the audio signal level drops below
the attack level, the DRC stops reducing the volume. The rate of decrease is
programmable via the attack rate. The DRC increases the audio signal level again when it
drops below the release level. This level is based on the audio RMS-value and is related
to the attack level. The rate of increase is programmable via the release level. The DRC
stops increasing the volume when the audio signal level reaches the release level or the
DRC volume falls to 0 dB.
Figure 13
Fig 12. DRC feedback design
•
•
•
•
Attack level
Attack rate
Release level
Release rate
shows the attack and release behavior of the DRC.
volume control
setting
All information provided in this document is subject to legal disclaimers.
audio in
Rev. 02 — 15 October 2010
Figure
12.
Mono BTL class-D audio amplifier with digital input
DRC volume
PARAMETRIC
EQUALIZER
5-BAND
DRC
LIMITER
BASS AND
CONTROL
TREBLE
RMS
010aaa550
TFA9879
© NXP B.V. 2010. All rights reserved.
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