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Audio is almost always a continuous waveform, so the results of interpolation are good enough for musical use; it’s nearly impossible to hear a single error. However, if a tape is in not in perfect condition or the deck’s heads haven’t been cleaned recently, you might have enough errors to cause a general degradation of audio quality, which passes on to any copies you make—digital or analog. Some DAT machines and MDMs display the current error rate. If yours does, monitor it from time to time.
So far I’ve only covered minor imperfections in digital dubs. Some problems can be more severe. For instance, if a DAT tape has too consecutive many errors, the error correction may not work at all, and you’ll hear digital noise instead of your recording.
Jitter is another issue. As I discussed previously, it shouldn’t affect purely digital connections. AES standards specify maximum allowable jitter on output and minimum jitter tolerance on input, which defines the greatest amount of jitter that the input signal can include and still be received properly. The current standard specifies a minimum jitter tolerance of several times the maximum output jitter to allow for chains of devices and maximal interoperability. Devices that conform to these standards shouldn’t have jitter-related difficulties. Not all devices meet the necessary specs, however, and some older devices may have been built prior to the adoption of the current standards.
If a device has extremely high jitter at its digital output or if the device receiving the data can’t handle much jitter at its input, their communication can fail, causing pops, clicks, and other artifacts. That holds true for connections between all digital devices, including digital audio workstations (DAWs), sound cards, and effects processors.
Likewise, digital cables can fall prey to most of the same gremlins as their analog counterparts, including loose connections, defects, and impedance mismatches. You can always get errors in DAWs from disk-related problems (such as buffers set too small), or processor spikes caused by brief overloads in system activity.
Finally, many digital-audio glitches—clicks, pops, low-level “fizz,” and the like—can be caused by a simple problem: improper word-clock settings. Two devices that are connected digitally but are not in agreement on the same word clock form a recipe for real trouble. In my experience, this is the source of many erroneous complaints that digital transfers are error prone. If you merely ensure that all connected devices agree on a single word-clock master, you can eliminate this common headache.
In summary, to ensure premium digital dubs, keep tape heads clean, preserve media (such as DAT tapes) in safe storage environments, set word clocks correctly, pay attention to error rates, take the same care with digital cables as you would with analog cables, make sure that your equipment has reasonable jitter characteristics, and set your DAW buffer sizes conservatively. As long as you take those precautionary steps, you can expect digital dubs to work well.
One other point you should keep in mind is to always monitor while you dub, just as you would with analog tape. Your ears should be your final reference. Remember, the recording you save may be your own.
Myth No. 7: All digital synths and effects sound the same. This myth is also known as: All digital EQs sound the same, All virtual analog synths sound the same, and All digital compressors stink. This is as true for digital gear as it is for analog gear, which is to say, not at all.
With analog devices, you have great-sounding EQs and lousy-sounding EQs. What’s more, a couple of great-sounding EQs (or compressors or synthesizers) may sound totally different from each other. It should be no shock that the same situation exists for hardware and software in the digital domain.
What makes a good or bad digital EQ, compressor, filter, or oscillator? Many issues of digital-audio quality arise from one source, and it happens to be one of the major differences between analog and digital audio: frequency range. Analog audio has a theoretically infinite frequency range, whereas digital audio (software and hardware) has a hard limit on high frequencies, as determined by the sample rate.
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Reprinted with permission from
Magazine, May, 2001© 2000, Intertec Publishing, A Primedia Company All Rights Reserved
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