Lavry 3000S Operation Manual page 23

Appendix I
AUDIO PRECISION FFT AMP1(dBFS) vs FREQ(Hz)
-100.0
-105.0
-110.0
-115.0
-120.0
-125.0
-130.0
-135.0
-140.0
-145.0
-150.0
-155.0
-160.0
-165.0
-170.0
-175.0
-180.0
20.00 2.02k 4.02k 6.02k 8.01k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k 22.0k 24.0k
Fig. 4 - Acoustic Bit Correction
16 (top), 18, 20, and 22 bits
no input signal
Acoustic Bit Correction may be used with words of lengths wider than 16 bits. Figure 4 shows
the noise floor of Acoustic Bit Correction (High Pass, NS2) without a signal at 16, 18, 20, and
22 bit wordlengths. Note the curved noise-floor with lowest level in the ear's most sensitive
mid-range region.
Figure 5 shows Acoustic Bit 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.
AUDIO PRECISION FFT AMP1(dBFS) vs
-80.00
-85.00
-90.00
-95.00
-100.0
-105.0
-110.0
-115.0
-120.0
-125.0
-130.0
-135.0
-140.0
-145.0
-150.0
-155.0
-160.0
-165.0
-170.0
20.00 2.02k 4.02k 6.02k 8.01k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k 22.0k 24.0k
Fig. 7- 16 bit input signal -100 dB
truncation by previous processing
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.
14 NOV 93 12:54:19 AUDIO PRECISION FFT AMP1(dBFS)
-100.0
-105.0
-110.0
-115.0
-120.0
-125.0
-130.0
-135.0
-140.0
-145.0
-150.0
-155.0
-160.0
-165.0
-170.0
-175.0
-180.0
20.00 2.02k 4.02k 6.02k 8.01k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k 22.0k 24.0k
Fig. 5 - ABC HP-NS2
16 (top), 18, 20, and 22 bits
-120 dB 1 kHz sine tone
FREQ(Hz) 14 NOV 93 15:50:12
vs FREQ(Hz) 14 NOV 93 12:45:07 AUDIO PRECISION FFT
-100.0
-105.0
-110.0
-115.0
-120.0
-125.0
-130.0
-135.0
-140.0
-145.0
-150.0
-155.0
-160.0
-165.0
-170.0
-175.0
-180.0
Fig. 6 - dither only
16 (top), 18, 20, and 22 bits
-120 dB 1 kHz sine tone
AUDIO PRECISION FFT AMP1(dBFS) vs
-80.00
-85.00
-90.00
-95.00
-100.0
-105.0
-110.0
-115.0
-120.0
-125.0
-130.0
-135.0
-140.0
-145.0
-150.0
-155.0
-160.0
-165.0
-170.0
20.00 2.02k 4.02k 6.02k 8.01k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k 22.0k 24.0k
Fig. 8- 16 bit input signal -100 dB
additional processing and truncation
LE3000S
AMP1(dBFS) vs FREQ(Hz) 14 NOV 93 12:47:26
20.00 2.02k 4.02k 6.02k 8.01k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k 22.0k 24.0k
FREQ(Hz) 14 NOV 93 13:58:03
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