Post
by Khazul » Thu May 26, 2011 3:26 pm
Positive side for high sampling rates:
- raises the Nyquist frequency which means reflected overtones from quantising errors during sampling will have diminished to near nothing by the time they impact the audible spectrum, but see the consideration below.
- Do to above, you generally get slightly cleaner sonds from synths and audio processing as you at less at the mercy of randomly good or poor bandwidth limiting and/or anti-aliasing algorithms on whatever synths and processors you use (assuming they have any at all) and particularly less at the mercy of artefacts from non-oversampled slice/grain type processing of audio.
Negative side:
- do you really want to work at such a high sample rate? It requires proportionately more computing resources of all kinds - CPU speed, memory bandwidth, I/O bandwidth to storage. Working at 96K or 192K for eg might mean you are having to freeze bounce alot to keep your computer useable. Bouncing/freezing is a trace off - it trades CPU use for I/O and cache memory use (stream pre-calculated audio instead of real time calculating it). At very high sample rates, your computer may not be able to deal with the I/O side of that trade off.
- eventually you have to sample rate convert back down - so choose you sample rate converter tool carefully if you want to fully gain from recording and working at a high sample rate. A shitty sample rate conversion can easily undo all that effort and pain.
Something to consider:
A modern analog to digital converter uses various techniques to minimise quantising errors anyway. For example, a modern fifth order delta-sigma ADC that can deliver an SNR of 160dB is probably using 64x over sampling - when sampling to 44.1KHz - that equates to the audio signal being effectively sampled at 2.8MHz or so and because of the error/noise shaping that goes on in such converters its actually equivalent to the performance of a dumb ADC operating at a way higher oversampling amount in the order of millions. Because the effectively initial sample rate is so high, then the Nyquist frequency is also extremely high leaving a huge gap between the sample rate limit and the actual filtered output spectrum. Having a huge gap mean a much cleaner and more easily constructed filter can be used to finally deliver the digital signal at the desired bit rate.
So, going back to to reason for using a very high sample rate:
If you record at 192K, then SRC down to say 44.1 before mixing/processing etc - then its net loss due to the use of SRC with a high quality initial converter.
If you record at 192K then stay at 192K for all processing, then finally use a high quality SRC to get down to 48/44.1K as required then its a net gain *if* your computer can handle it.
If you record at 44.1K, then quality SRC up and do all you processing at an exact binary power multiple (say 4x = 176.4K) then finally use a good SRC to get back down again, then its a net gain *if* the processing plugins you are using support the high sample rate and work well at that sample rate as effectively you are exploiting end to end oversampling.
In every day practice - many modern high quality plugins (especially those associated with dynamics/transient and EQ processing) might offer option of oversampling (but even oversampling can be done well or badly), or internally employ oversampling to minimise unwanted distortion/noise, so the benefits of working at a high sample rate are small. With typical careful use of high quality EQ in a well controlled mix, then they may even disappear to nothing. Poorer plugin that can still work properly at a high sample rate OTOH will benefit more from it.
Is it worth the pain though for the marginal gain? IMHO if you have a must-use plugin that has a shitty high end, then there are some plugin oversampling plugins around that allow the shitty plugin to get its own over-sampling wrapper and that might help is the SRC on either side is of decent quality.
Nothing to see here - move along!