[sdiy] jitter analysis

[Czech Martin]

I always thought that a sliding DTF IS equivalent to a filter bank,
but with a strange impulse response for each channel.

The discussion shows that even a "simple" problem of measuring and
analysing the properties of old hardware is getting complicated, the
more thought is spend on it.

No wonder that current emulations are far of the original.

m.c.

> -----Original Message-----
> From: Magnus Danielson [mailto:cfmd at bredband.net]
> Sent: Freitag, 9. Juli 2004 19:10
> To: Czech Martin
> Cc: ifrc at iar.se; synth-diy at dropmix.xs4all.nl; jschmitz at schmitzbird.de
> Subject: Re: [sdiy] jitter analysis
> 
> 
> From: "Czech Martin" <Martin.Czech at Micronas.com>
> Subject: RE: [sdiy] jitter analysis
> Date: Fri, 9 Jul 2004 15:51:24 +0200
> Message-ID: 
> <D9D56E8FA1A73542BE9A5EC7E35D37FF01C4EFBF at EXCHANGE2.Micronas.com>
> 
> > > The ear, being a bandpassesque analyserbank, can naturally 
> > > sniff the sidebands,
> > > but some of it will be masked by normal masking procedure. 
> > > Analysis done by
> > > among others the late Julian Dunn has provided insight into 
> > > where a jitter
> > > tolerance curve would be given the knowledge we have about 
> > > masking effects and
> > > hearing the sidebands. (I am actually missing the paper, so 
> > > if someone digs it
> > > out, let me know). This tolerance curve goes below the ns 
> > > level, just to give
> > > you an indication... I don't recall it in detail right now.
> > 
> > 
> > and the same thing can the DFT do to a sampled version of 
> the signal,
> > since the side bands will all be there.
> > I think the reall con against the spetral measurement is
> > its slowness. I have to average somehow and then I loose 
> track of the
> > short time changes. Heisenberg biting again.
> > 
> > But what about Parsevals theorem? Can't that help?
> 
> First of all, a DFT is _NOT_ equalent to a filterbank. A 
> filterbank with
> filters have a certain transientresponce of their own, but 
> the detector
> mechanism weighs in and this is not necessarilly RMS as DFT 
> provides with
> propper scaling. A continous time filterbank has detectors 
> providing continous
> time monitoring and in the ear also the continous time 
> correlation of the
> detectorsignal. This correlation excists and for instance the 
> masking effect is
> one of the results of this correlation.
> 
> Going straight to the DFT is not supported by what we know 
> about the hearing to
> start with. Again, doing models is easy, verify their 
> validity to real life is
> much much harder. The quick and dirty engineering assumption 
> of tossing a DFT
> on a problem is not allways even a wise thing to do, you can 
> end up analyzing
> all the wrong artifacts.
> 
> Also, when trying to do more fundamental research one has to 
> be carefull not to
> waste the wrong type of data, but the hole purpose is to 
> establish what makes
> it tick and only when you do that you know which shortcuts 
> you can do. Much
> work actually become useless due to lack of methology or lack 
> of analysing the
> methology. Looks darn nice on the paper, but when you really 
> think about it at
> least I end up thinking how much efforts where wasted for the 
> poor addition to
> knowledge. That accounts for so many articles a year that I 
> get really scared!
> 
> Cheers,
> Magnus
> 
> 
>