dCS 974 User Manual | Manual for Software Version 1.0x |
dCS Ltd | May 2001 |
The 0 dB reference level is taken as the minimum noise we could 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.
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 present29.
| Truncation Type, with | Noise, | Noise, | Comments |
| 44.1 kS/s data rate | unweighted, | F weighted, |
|
| rel 16 bit Q | rel 16 bit Q |
|
| noise30 | noise |
|
16 bit truncation | 0 dB | 0 dB | Unpleasant low |
16 bit truncation with |
|
| level effects |
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 2nd |
|
| penalty |
6.2 dB | Okay with input | ||
order noise shaping and |
|
| noise floors down |
no dither |
|
| to |
16 bit truncation with 2nd | 11.0 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 | Okay with input | |
order noise shaping and |
|
| noise floors down |
no dither |
|
| to |
16 bit truncation with 9th | 28.2 dB | Unconditionally free | |
order noise shaping and |
|
| from truncation |
Noise Shaped |
|
| effects with all |
Triangular dither |
|
| inputs |
Table 16 – Dither and Noise Shaping Noise Powers
29DSD 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.
3016 bit Q noise is
Manual part no: DOC1241121A1 | Page 105 | Document No: |
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