4/1/2023 0 Comments Word clock sync![]() ![]() ![]() The amplitude error caused by the jitter is shown in red.If the clock is jittery in an A-D converter, for example, then the analogue audio waveform is likely to be measured at the wrong moments in time - either slightly too early or too late, relative to the correct sampling instants. Jittered samples in relation to the required sampling instants. This problem is known as jitter, and it affects many different aspects of digital audio systems, but is of particularly critical importance in A-D and, arguably to a less critical extent, D-A conversion.įigure 1. If this reference clock is not particularly stable then the interval between samples - which should be absolutely precise - will vary. Without doubt, the major difference between high-end and budget converters is the quality, stability, and consistency of the internal clock circuitry - the part that determines when a sample is taken. Having said that, the almost universal use of oversampling and delta-sigma topologies has reduced the performance differential in that regard enormously in recent years. High-end converters will certainly have better analogue circuitry, though, and the sampling and quantising sections of the converter are likely to be more accurate and consistent. It is reasonable to assume that the more expensive converters will do a better job of this critical A-D process than budget converters, and all other things being equal this is generally true - although the differential is small and getting smaller all the time. So, that means choosing an appropriate sample rate and bit resolution, and setting the analogue signal level so that true signal peaks don't exceed the maximum level of the converter. Mess that conversion up and there is absolutely nothing you can do to recover the original quality. It is the A-D conversion process which defines the quality of a digital signal. The most important part of the paragraph above is the phrase 'once an analogue signal has been digitised'. ![]() Sure, in all these cases there will be very significant operational differences, and there may be reliability and maintenance issues, but basically the audio quality is locked into a digital signal, and you can't accidentally mess that up. Once an analogue signal has been digitised, there is no fundamental reason why a £1000 digital mixer should sound any different to a £250000 digital mixer, or a top-flight Sony 3348 multitrack should sound different to an Alesis hard disk recorder. The very nature of digital audio has changed all that, though. In the analogue world, you pretty much got what you paid for: the highest-quality products were extremely expensive - the old law of 'diminishing returns' applied in a very audible way - and cheap products usually sounded, well, not too good usually! And, whereas a decade and a half ago such equipment was the costly preserve of professional studios and mastering rooms, today digital mixers and signal processors are available at almost bargain-basement prices. It is probably fair to say that the vast majority of audio is recorded, manipulated, post-produced and replayed using digital audio equipment of one form or another. Most home studio owners now rely heavily on digital audio recording and processing, but you could be sacrificing the quality of your recordings if your system isn't clocked correctly.
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