[LAU] Building a DAW

[Fons Adriaensen]

On Tue, Jun 02, 2009 at 04:56:44PM -0400, Ricardus Vincente wrote:

>  When you say Vari-Speed do you literally mean changing the speed of the
> analog deck, or are you referring to the normal wow-and-flutter of an
> analog tape machine?

The speed of an analog tape machine may be very stable in the short
term (i.e. no wow or flutter) but it is never exact, and can have
small variations that depend on things like line voltage, temperature,
ageing, and the phase of the moon.

Suppose you record a song using both the analog machine and
Ardour. The analog machine's speed is nominally fixed but will
have some small error. Ardour's sample clock is also nominally
fixed but will also have some small error. And these two errors
are not linked togehter in any way.

So the next day these small errors will be different, and even
if you start both systems exactly synchronised they will not
remain in sync. Assume the difference is 0.1 percent, one in
a thousand. That means that after three minutes there will be
a difference of 1/5 of a second, which is just too much.

There are two aspects to syncing: on is 'chasing, making
one machine follow the transport movements of the other -
if you fast wind the analog one then Ardour will follow.
The other is keeping them at exactly the same speed. 
The speed of analog machines can be controlled easily,
For digital it means either changing the sampe clock or
resampling the signal to match a fixed sample clock. 

Ciao,

-- 
FA

Io lo dico sempre: l'Italia è troppo stretta e lunga.