Power Driver Integrated Full Digital Audio Amplifier
NTP-8230
9. PRE-PROCESSING
9.1. Pre Bi-Quad Filter Chain
NTP-8230 has two kinds of Bi-Quad filter chains. One is Pre Bi-Quad filter chain and the other is Post
Bi-Quad filter chain for bass management, loudness control, loud-speaker EQ, etc.
The former is called pre Bi-Quad filter chain and two 2nd order floating point Bi-Quad filters are
connected serially to all the three channels. The structure is shown in Figure 13.
0
0
0
0
0
0
CH 1
CH 2
CH 3
BQ1
BQ1
BQ1
BQ2
BQ2
BQ2
1
1
1
1
1
1
Figure 13. Pre Bi-Quad Filter Structure
Filter coefficients are 32-bit floating point numbers and can be downloaded thru I2C interface. To
download the pre Bi-Quad filter coefficients to internal memory of NTP-8230, designer should change
the flags of register Address 0x7E to „enable coefficient write‟ status.
When CH1(or CH2 or CH3) Flag of register Address 0x7E is set to 1, BQ ROM Address 0x00~0x04
designates coefficients of 1st pre Bi-Quad filter chain of channel 1(or channel 2 or channel 3) and
indicates b0, b1, b2, a1, a2 respectively. BQ ROM Address 0x05~0x09 designates the coefficients of
2nd chain of channel 1(channel 2 or channel 3).
The Bi-Quad filter structure is shown in Figure 14.
b0
x
+
b1
a1
Z-1
x
Z-1
x
b2
a2
Z-1
x
Z-1
x
Figure 14. Bi-Quad Filter Structure
9.2. 3D Surround
3D surround expands the sound field of two channel stereo to the extent that is wider than the actual
speaker spacing. Because this feature is acoustically valid for two channel signal, no other channels
except channel 1/2 have this internal block.
NTP-8230 realizes the 3D effect by combining delay and band-pass filter. At first, define the size of
delay by using register Address 0x0D. Possible maximum delay is 40 samples delay and this is about
0.4msec based on 96kHz signal input.
And then download the band-pass filter coefficients to internal memory of NTP-8230 (same with the Bi-
Quad filter coefficient download procedure). The BPF is two 2nd order IIR filter. Each channel can
have different BPF. Change the 3D flag status of register Address 0x7E to „enable coefficient write‟
status and write the actual coefficient values to ten register Addresses 0x0A~ 0x13. Also, internal 2x2
mixer helps ease of design. For using 3D mixer, download the gain values to two register Addresses
0x3C~0x3D.
Copyright ⓒ NeoFidelity, Inc.
Page 18
Document Number: DS8230 draft ver. 0.1
2011-01-11
ETC [ ETC ]
