
LB1
RB2
Atten
LB2
L
R
TOLEFTCHANNEL
TO RIGHT CHANNEL
SLAS497C – AUGUST 2006 – REVISED DECEMBER 2008 ............................................................................................................................................. www.ti.com
The coefficients for this filter implement a variety of sound effects, with bass-boost or treble boost being the most
commonly used in portable audio applications. The default N and D coefficients in the part are given in
Table 3and implement a shelving filter with 0-dB gain from dc to approximately 150 Hz, at which point it rolls off to a
3-dB attenuation for higher frequency signals, thus giving a 3-dB boost to signals below 150 Hz. The N and D
coefficients are represented by 16-bit twos complement numbers with values ranging from –32768 to 32767.
Table 3. Default Digital Effects Processing Filter Coefficients,
When in Independent Channel Processing Configuration
Coefficients
N0 = N3
D1 = D4
N1 = N4
D2 = D5
N2 = N5
27619
32131
–27034
–31506
26461
The digital processing also includes capability to implement 3D processing algorithms by providing means to
process the mono mix of the stereo input, and then combine this with the individual channel signals for stereo
output playback. The architecture of this processing mode, and the programmable filters available for use in the
system, is shown in
Figure 26. Note that the programmable attenuation block provides a method of adjusting the
level of 3D effect introduced into the final stereo output. This combined with the fully programmable biquad filters
in the system enables the user to fully optimize the audio effects for a particular system and provide extensive
differentiation from other systems using the same device.
Figure 26. Architecture of the Digital Audio Processing When 3D Effects are Enabled
It is recommended that the digital effects filters be disabled while the filter coefficients are being modified. While
new coefficients are being written to the device over the control port, it is possible that a filter using partially
updated coefficients may actually implement an unstable system and lead to oscillation or objectionable audio
output. By disabling the filters, changing the coefficients, and then re-enabling the filters, these types of effects
can be entirely avoided.
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