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Q. Will copying digitally between Minidiscs reduce the sound quality?

By Matt Bell, Mike Senior & Tom Flint
Published September 2000

If I make a digital copy of one Minidisc recording onto another Minidisc, will the data compression reduce the quality of the copy or will it simply make a clone without further data reduction?

Brian Fairman

Tom Flint, Matt Bell & Mike Senior reply: Apart from some professional Minidisc duplicators (see below), all Minidisc recorders impose their patent ATRAC data compression whenever they record, even if you record using a digital input. This means that if you copy from one Minidisc to another then the music data will have been compressed twice. ATRAC works on psychoacoustic principles by discarding frequencies that it is unlikely the average human ear will miss in a mix, but precisely because the calculations involve concepts like 'the average human ear', its effects are more audible to some people than others, and this is true of its cumulative effects, too. You might find it interesting to successively copy a recording from Minidisc to Minidisc to see how many generations it takes before you find the degradation in sound quality unacceptable.

CDs and DATs do not use data compression so, in theory at least, you can make endless digital copies without any loss of quality. You could therefore theoretically make digital clones of your Minidisc recordings onto CD, if you want to back up your Minidisc masters. In practice, this may not work, because consumer Minidisc machines implement the dreaded digital copy protection system SCMS, which prevents more than one digital copy of any recording being made, supposedly to protect copyright. Unfortunately, even though there is no infringement when you are copying your own material, there is no way to explain that to the SCMS system in your Minidisc! There are high‑end professional Minidisc machines which do not implement SCMS and can create digital Minidisc clones which bypass the data compression. You can tell if you have one of these machines by looking for special 25‑pin D‑Sub 'Duplication' ports on the back of your Minidisc machines. Needless to say, such machines are expensive (one typical model retails for £2500) and most consumer models do not offer this facility.