Tuesday, November 4, 2014

Recording CDs To Cassette For A Better Sound Quality?

To those old enough, do you still remember the time when music on CDs tends to sound better when they are recorded onto blank cassette tapes? 

By: Ringo Bones 

Let’s face it early 1980s era CD players may have been built like a tank – like that of cassette tape decks of the period. But when compared to contemporary universal disc players that can play CDs DVDs or any 5-inch diameter disc, the sound quality of early 1980s era CD players leaves much to be desired. Even though in the 1990s we finally have names on the “audio gremlins” that plague the Redbook Spec 16-Bit, 44.1-KHz digital audio – data induced jitter for example – why is it that early 1980s era CDs sound quality improves once it is transferred to cassette tapes, 8-Track, Elcaset or any other analog magnetic recording media? 

Even during the Golden Age of Stereo, audio engineers and audiophiles already know that high-order very steep cutoff low pass and high pass filters are deleterious to perceived sound quality. The reason why CDs – and even low data rate MP3 audio files – tend to sound better when recorded on analog magnetic media like cassettes, Elcaset, 8-Track, etc, is that analog magnetic tapes doesn’t require a high order low pass filter as an “anti-aliasing filter” to remove signals that doesn’t fit in to the Nyquist Criterion of Redbook Spec CDs. Any signals too high in frequency to be recorded in analog magnetic recording media just rolls off gently at a rate of 6 dB per octave. 

Why early CD players tend to sound worse than their more contemporary counterparts is because anti-aliasing filters with very good subjective sound quality were very difficult to design back in 1982. It was Philips of Eindhoven, Netherlands that were the first to come up with an oversampling digital filter – which is all about digital signal processing algorithms – that resulted in a better sound quality than competing anti-aliasing filters of the time, but digital signal processing was still at its infancy in comparison to what we can do during the 1990s never mind today. While Sony in Japan struggled on with impractical ninth-order analog brickwall filters, Philips had no choice as they were unable to make reliable 16-bit converters at the time of the CD’s 1982 CES debut. 

By using oversampling and noise-shaping way back in 1983, Philips could make their proprietary 14-bit converter for 16-bit 44.1-KHz Redbook spec CD work with 16-bit resolution. Even though both Philips and Sony’s CD players costs around 750 US dollars once they became available back in 1983, a similarly priced machine in the mid 1990s can easily show it a clean pair of heels sound quality wise. Today’s similarly priced machines are even better. Would the hi-fi cassette tape decks role during the early days of CD is a “widely available digital-to-analog-converter to make early CD sound better”?