AD122-96 MX
Appendix I
14
Figure 5 shows
α
coustic
β
it Correction™
(High Pass, NS2) applied to a 24 bit input, reducing to 16,
18, 20, and 22 bit output widths. Notice that there is no noise modulation present.
Figure 6 shows the effect of high-pass triangular dither only. The more coherent data in the dithered
bits, the better the dithering process works. Note that dithering from 24 bits to 22 bits has a lower noise
floor but more visible distortion components than dithering to a shorter word length, due to fewer bits
in the portion of the word being truncated.
Fig. 7- 16 bit input signal -100 dB
Fig. 8- 16 bit input signal -100 dB
truncation by previous processing
additional processing and truncation
Should dither be applied to input signals of 16 bit word length? Figure 7 shows a -100 dB tone of 16
bit word width with no dither or noise shaping. Note the presence of all of the odd harmonics, created
when the truncation process turned the tone into a 1 lsb square wave. Figure 8 shows the result of
applying additional processing to this signal, and truncating the result, thereby creating additional
distortion components.
Fig. 9-
16 bit input signal -100 dB
Fig. 10- 16 bit input signal -100 dB
high pass dither applied
Acoustic Bit Correction applied
Figure 9 shows the original 16 bit input signal processed with high-pass dither only. Notice that the
additional distortion is gone. Figure 10 shows
α
coustic
β
it Correction™
(dither and noise-shaping)
applied to the same signal with an increase in the effective noise floor.
α
coustic
β
it Correction™
cannot remove truncation distortion in an incoming 16 bit signal, but it can avoid additional truncation
distortion if additional processing, such as sample rate conversion, has been applied.
