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To continue where we left off in the first part of this article, the speed and capacity of digital systems is continuously improving, making higher sample rates and more bits plausible alternatives to frustrating methods of perfecting digital recordings. The ability to use higher sample rates and more bits is making digital recordings sound exceptionally better than they ever have in the past. Because the speed of computers has increased drastically over time, complex mathematical processes can now be applied to signals, to remove the unwanted frequencies, after the signal has already been digitized. This is a collection of processes, known as “oversampling,” which allow for a high-speed sampling rate. Therefore, it is wise to opt for a higher sampling rate; ensuring better quality sound by oversampling and avoiding the brick-wall. When you choose to modify the sampling rate by increasing it, you then have the option to use a gentler low pass filter, rather than the steep brick-wall filter. This is because oversampling pushes the aliases further from the audible range. Additionally, when the digital signal is re-sampled within the digital domain, to produce an output stream at the required sample rate of 44.1kHz, this is known as decimation. Employed as a means of oversampling, the decimation process doesn’t ignore the samples it doesn’t need. Instead, it effectively takes the extra information obtained from oversampling the signal, and turns it into increased bit-resolution. Increasing the number of bits used to quantize the analog signal will result in a more accurate recreation of the input, but the increased accuracy, obviously, will also mean more data to store. The amount of oversampling you need depends on two things: the highest frequencies present in the signal you are processing (as mentioned earlier), and how much harmonic distortion is created by the process. To better explain: if you were processing a bass guitar, the harmonics created will probably not be high enough to cause foldover, or aliasing. If, however, you were processing high frequency symbol crashes, you may need increased oversampling to avoid the brittle harsh quality produced by the aliasing distortion. However, oversampling, alone, will not suffice to provide the kind of noise performance required in a professional system. And so, noise-shaping is another digital filtering option that can be employed to redistribute and equalize the quantizing noise, so that it is reduced in the desired audio band and increased in the frequency spectrum. In conclusion, with the introduction of more capable technology, there is an ever increasing blur in distinction between analog and digital recordings. However, it’s safe to say that having a copy of each wouldn’t be too bad. Just keeping digital back-ups of your analog recordings can save you a lot of headaches in the future; especially if your records and tapes become damaged. If you happen to have damaged records or tapes, please see my articles on how to fix them. If your records and tapes are in good condition, then now is the time to make digital back-ups. If you don’t have the equipment to perform an audio transfer, I recommend Two Squares, a Minneapolis media conversion shop that offers audio and video transfer and image scanning services.
Two Squares, Inc
6272 Boon Ave N.
Brooklyn Park, MN 55428
763-400-4510
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