Popular Post tailspn Posted May 2, 2017 Popular Post Share Posted May 2, 2017 As formats, DSD has +6dB greater dynamic range than PCM. DSD and PCM are digitally storable formats to record and transmit analog signals, mostly audio for our interest. 0dB is a definition in recording to signify a maximum level not to be exceeded. Below 0dB, both PCM and DSD are capable of the same signal level range, better known as dynamic range. Both can express an infinitely small signal, far below the practical minimal signal transferable by practical analog electronic circuits. In the case of PCM, 0dB represents the maximum binary range that the the format can represent; there's no bits left. It's a 2's compliment binary word for each sample that's either all 1's, or all 0's at 0dB (full scale). It's 2's compliment to support both positive and negative values. In DSD, there are no values represented. It's the density modulation of a bit clock, who's percent of modulation is proportional to the signal level, not a numerical value of a signal level (at an instant in time). All of that is background to the fact that from the lowest signal level deliverable to a A/D converter to the maximum that produces 0dB, the same dynamic range is expressible in both a PCM or DSD format up to 0dB. The DSD format however has an additional +6dB of headroom above 0dB that is not achievable with PCM. That's because DSD 0dB is specified as 50% modulation, allowing an additional 6dB of signal level to be represented. ferenc, johndoe21ro, look&listen and 1 other 2 2 Link to comment
tailspn Posted May 2, 2017 Share Posted May 2, 2017 You're right! As long as the infinitely loud signal does not exceed the full scale range of PCM (0dB in DSD is the same level as 0dB in PCM), then the DSD representation will have +6dB additional headroom. AND BEYOND! Link to comment
Popular Post tailspn Posted May 2, 2017 Popular Post Share Posted May 2, 2017 4 hours ago, mansr said: In practice, both PCM and DSD are capable of representing the full signal range between the analogue noise floor and the maximum analogue level. The 6 dB headroom of DSD is an implementation detail and should be ignored for the purposes of this discussion. I agree about the capability of both representing the full signal range, but for me as a recording engineer, the practical application is the most important difference. The performance of currently available professional quality A/D converters yields better than 145dB dynamic range from its quantization noise floor to 0dB full scale. Since there are no direct PCM A/D converters (all are Sigma-Delta Modulator front ended), PCM is derived from the 1-bit, or more likely multi-bit Pulse Density Modulated bit streams from the modulator(s), and therefore can not possibly possess greater dynamic range. To your point though, today's recording systems, regardless of whether outputting DSD or PCM, they have a greater dynamic range that the analog signals being fed them. Actually, by 20 to 30dB. So the positioning of the signal dynamic range within the recorders dynamic range is a recording/mastering engineer choice. The practical difference between DSD and PCM affecting that signal placement is the distortion performance when approaching the loudest recorded signal. PCM hard clips at 0dB with minimal distortion. DSD soft clips, like tape, with the 0dB level specified halfway up the modulation scale (50%), and the distortion performance still very acceptable. But like tape saturation, the distortion artifacts of DSD increase rapidly when approaching 100% modulation (+6dB) The +6dB headroom offered by DSD versus PCM is not a measure of DSD superiority, or an "implementation detail", but a practical consideration when making music recordings. Recording and mastering engineers aim at crowding 0dB to obtain the maximum loudness. In acoustic music recording, the ability to overshoot in DSD by almost double the signal level on occasional music peaks is a big asset. It's like having the effect of compression without having to compress. The lowest level signals can be effectively presented at a higher level without clipping the highest level. The DSD +6dB headroom is very much available and used in wide dynamic range acoustic music recording, although most recording/mastering engineers will avoid exceeding +3dB. jabbr, orresearch and blue2 3 Link to comment
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