Sony's Playstation 2, announced and released with such fanfare a few months back, contains a digital audio amplifier courtesy of Tripath. Sony's new VAIO (Video Audio
Integrated Operation) note-book computers also contain a similar digital audio amplifier.
When Compact Discs burst onto the audio scene in the early
1980s, they quick-ly changed the definition of ‘hifi’.
Suddenly we had a recording and playback technology which could
deliver a signal-to-noise ratio of 96dB, distortion levels below 0.01%,
negligible wow and flutter and a frequency response which was near enough to
‘ruler flat’ over the complete audible spectrum.
CDs delivered these benefits mainly because they took advantage
of digital technology. Instead of trying to record audio waveforms faithfully in
the grooves cut into vinyl records, they ‘sampled’ the waveform 44,100 times per
second and turned it into a stream of binary numbers – ones and zeros – which
could be recorded and played back much more faithfully. This made it possible to
reconstruct a much more accurate replica of the original, when the digital
samples were converted back into analog form.
The same sort of benefits came when digital technology was
applied to tape recording to provide us with DAT (digital audio tape). And the
improvements continue, with the new enhanced digital recording techniques such
as HDCD (High Definition CD), SACD (Super Audio CD) and DVD-Audio – which are
just coming onto the market.
But until very recently, the high quality audio available from
these digital technologies still had to be converted back into analog for the
last crucial step in the audio chain: power amplification to drive the speakers.
That’s because up till now, analog circuitry has provided the only way to
achieve a high-quality audio power amplifier.
Even today, some audiophiles will tell you that the only kind
of power amplifier worth listening to is one with a class A (or at worst, class
AB) push-pull output stage, with a whopping great power supply, plenty of
heatsinking and loads of negative feedback.
And there’s the rub: traditional high quality analog power amps
and their power supplies are big, heavy, expensive and wasteful of power.