ACS422A68TAGZBX8 IDT, ACS422A68TAGZBX8 Datasheet - Page 31

• Manufacturer Part Number: ACS422A68TAGZBX8
• Description: Interface - CODECs
• Manufacturer: IDT

Specifications of ACS422A68TAGZBX8

• Rohs: yes
• Part # Aliases: IDTACS422A68TAGZBX8

ACS422x68
LOW-POWER, HIGH-FIDELITY, INTEGRATED CODEC
©2011 INTEGRATED DEVICE TECHNOLOGY, INC.
3.11. Treble Enhancement
One of the mechanisms used to limit the bit rate for compressed audio is to first remove high frequency information
before compression. When these files are decompressed, this can lead to dull sounding audio. The IDT treble
enhancement replaces these lost high frequencies.
The enhanced treble function works much like the enhanced bass, however it's intended use is different. The enhanced
treble uses a non linear function to add treble harmonics to a signal that has limited high-frequency bandwidth (such as
a low bit rate MP3). In this case, the algorithm makes use of the audio fact that presence of audio between 4-8K is a
good predictor of audio between 10K-20K.
This implementation extracts the high frequency content that is available in the audio, generates harmonics of those
frequencies. These harmonics are then summed back into the original signal, providing a brighter sound.
This algorithm has 4 components.
1. Extract filter – This filter extracts the bass information that the speaker system can't reproduce.
2. NLF – This is a Nonlinear function that is used to generate the harmonics of the fundamentals in
3. Limit Filter – This filter will limit the amplitude of the harmonics generated to prevent the har-
4. Mixing – This structure allows mixing of the generated harmonics and the original material.
5. Cutoff Filter – This filter is used to remove all material below the cutoff frequency of the speaker
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This is a 4th order band pass filter with a typical bandwidth of 1.5 to 2 octaves.
the extracted audio. More on this function later.
monics from creating noise in the midrange. Too many harmonics will spill into the mid range
and be heard as unwanted buzzing. Too few and the psychoacoustic effect is not reached. The
exact composition of this filter is still or be determined. A 2nd order filter is currently sufficient for
the NLF function employed.
systems. This includes the fundamentals used to create the psychoacoustic effect, since they
can't be reproduced. This is a 2nd order high pass filter.
Extract Filter– This filter is used to extract the treble between 4-8K. This is 2 2nd order high
pass filters.
Enhanced Treble Non-Linear Function– Generates high frequency components
Limit Filter– This filter limits the harmonics generated by the NLF to prevent any significant
aliasing. A second order filter is sufficient.
Mixing Network – This simply sums the generated harmonic signals into the original signal.
Extract
Filter
Figure 12. Treble Enhancement
NLF
31
Limit
Filter
ACS422X68
V1.6 01/13