DCS dCS 904 rate, Noise, Noise, noise, lower, noise11, Comments, unweighted, F weighted, xTruncation Type, with 44.1 kS/s data

dCS 904 User Manual	Manual for Software Version 1.5x and 1.36
dCS Ltd	June 2000

possibly get away with – the amount that simple 16 bit truncation (16 bit Q noise) would give, if it were well behaved, which it is not.

xTruncation Type,	Noise,	Noise,	Comments
with 44.1 kS/s data	unweighted,	F weighted,
rate	rel 16 bit Q	rel 16 bit Q
	noise11	noise
16 bit truncation	0 dB	0 dB	Unpleasant low
			level effects
16 bit truncation with	3 dB	3 dB	Okay – can show
Top Hat dither			noise modulation at
			low signal levels
16 bit truncation with	4.8 dB	4.8 dB	All noise
Triangular dither			modulation and
			unpleasant effects
			removed, but noise
			floor is high
16 bit truncation with	4,8 dB	1.2 dB	All noise
Noise Shaped			modulation and
Triangular dither			unpleasant effects
			removed. Not much
			perceived noise
16 bit truncation with 3rd			penalty
	6.9 dB	-10.5 dB	Okay with input
order noise shaping and			noise floors down to
no dither			–102 dB
16 bit truncation with 3rd	11.0 dB	-9.2 dB	Unconditionally free
order noise shaping and			from truncation
Noise Shaped			effects with all
Triangular dither			inputs
16 bit truncation with 9th	23.4 dB	-17.9 dB	Okay with input
order noise shaping and			noise floors down to
no dither			–120 dB
16 bit truncation with 9th	28.2 dB	-16.7 dB	Unconditionally free
order noise shaping and			from truncation
Noise Shaped			effects with all
Triangular dither			inputs

Table 12 – Dither and Noise Shaping Noise Powers

Straight forward dither always adds noise – it can only produce signals with a noise floor higher than Q noise on its own. However, the noise power added is a few dBs for simple types. Noise shaping adds rather more noise, but it can be made to add it in parts of the spectrum that the ear is less sensitive to, so the perceived noise (F weighted noise) is lower – up to three bits lower. It results in a signal that the ear hears as having a far lower noise floor than a 16 bit truncated signal, rather than the “not much worse” of dither alone, even though there is really more noise present12.

1116 bit Q noise is -98.1 dB relative to a full scale sine wave.

12DSD carries this further. The principle is the same, but with DSD, there is more noise than there is signal, even at full scale. It is just that it is in a part of the spectrum the ear cannot hear.

Manual part no: DOC135904 iss 2B2 Page 65 135904ma2b2.pdf file available from website

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