All about DVD Part 4: DVD-Audio and SACD
When Audio-CD format emerged, most music producers and music
lovers were absolutely sure that Audio CD provides the best
quality sound possible and nothing else will ever be required.
However, some audiophiles instantly refused to accept new Audio
CD and reverted back to old vinyl disks. At first no-one took
them seriously, however, as the time passed an increasing number
of listeners started to notice, especially when comparing CD
albums with the same records on vinyl, that CDs are not capable
to transmit full range of sound. Eventually it becomes clear
that there are scientific reasons behind this, namely dynamic
range and sampling rate.
Dynamic range is the difference between the loudest and
softest sounds in audio record. Sound data is recorded on CD in
16-bit PCM format and therefore its dynamical range does not
exceed 96 decibels. And the upper range for human ear is 120Db.
The difference is obvious. While the lack of dynamic range might
be hard to notice for the pop music, but for something like
symphony orchestra sound engineers often have a problem with too
soft or too loud instruments which are beyond dynamical range
and therefore lost in record.
Apart from dynamic range it also became clear that Audio CDs
have insufficient sampling rate. Digital record consists
of small pieces called samples, each of them contains
information about sound in particular point in time. The more
samples are per unit of time, the higher is the quality of
record. Basically, sample is a digital analogue of sound
oscillation and for that reason they are measured by using the
same unit, hertz (Hz). The maximum frequency of sound that
humans can hear is around 20 thousands hertz (20 kHz). To
reproduce sound accurately, the sound information have to be
digitized with sampling rate higher than a human can hear.
During Audio-CD development it was believed that doubling this
rate - up to 44.1 kHz would be sufficient. But for some records
part of sound was lost and turned into noise. Especially often
that happened for classical music and jazz, with high-frequency
instruments such as violin and flute being the most unlucky
ones. It is scientifically proven now that for the most accurate
sound the sampling rate has to be not lower than 64 kHz. This,
of course, is far beyond Audio CD capabilities.
To address these issues the DVD-Audio format was
developed. It took more time to approve than DVD-Video, as