DeafinONEear wrote:
>
> Dan wrote:
> >You can proof your system by
> >reading a CDR back into the workstation digitally (synching to the
> >digital input), slipping the files into bit-synchronization, and
> >doing a subtraction test. If the files subtract to dead silence, the
> >CDR is good.
>
> To all those out there not in the know, how does one perform this test? D=
o
> you need dedicated software?
The really tricky part is getting the exact bit synchronization. It
sounds simple, but if anywhere in the whole business something was
running on a clocking rate that differed at all and produced new
samples, you will not get silence, but a beat frequency corresponding to
the difference in clocking. At least this is the case when a step
involves standard recording. Copying to a audio CD and then back should
avoid this problem as the sampling rate is already fixed. I ran into the
problem when trying to do a all digital subtraction test on the ATRAC in
the HHb Portadisc. I got to find out the difference between the system
clock on my G4 and the one in the HHb.
I've managed it from time to time, did some of it when setting up
testing of ATRAC 4, where I avoided clock problems by including a analog
step. There I put some obvious sample patterns at the beginnings of the
tracks, carefully edited the front end to the exact same sample, then
inverted one file (exchanged plus and minus at the waveform level) and
added the two files. It was all done using fairly standard tools
included in PEAK, which is the mac program I use for general sound I/O
and simple editing. I see no reason why that could not be done to test
audio CD recording.
I believe Dan has equipment where you can nudge the start point to get
the sync and run it in realtime. A bit less fiddly to set up.
It's also possible to use some file comparing programs if you do the
initial front end sync trim.
Remember to be accurate you have to be in exact sync, to the sample.
Figuring out how you'll do that is about all there is to it. The only
functions you need out of your editor other than sample by sample
cutting is a invert and adding two tracks. (or just subtracting one from
the other)
Walt
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