[hpsdr] sampling

[Terry Fox]

More likely  48kHz X2 = 96kHz
                   96kHz X2 = 192kHz

While 44.1 is common for CDs, the more common professional audio sampling
rates started as 32kHz (limited bandwidth), and 48kHz.  All three are
available on most professional DAT recorders (32, 44.1, 48).  The use of
multiples of 48kHz samplig grew out of oversampling the 48kHz.  One reason
was for better filter response, it is easier to make an audio filter flat
below, but cutoff above 20kHz if you oversample at 96kHz.  Then, the
oversampling kept going to 192kHz.

One must be careful when using these higher sampling rates, just because the
A/D can convert at 192kHz, that does not mean that the low-pass filter in
front of the A/D converter is flat to 1/2 that rate.  As the HPSDR group
found out when testing A/D converters, a 192kHz A/D may only pass audio (see
article in last year's ARRL/TAPR DCC).  There are other issues as well, such
as the speed and jitter of any sample & hold circuits, clock jitter,
dithering, and othrs that hve been mentioned elsewhere.

Now, we should have the best of both worlds.  The A/D that the Janus has not
only samples to 192kHz, but has a good frequency response on the input
low-pass filters, that allows us to actually use frequencies above the audio
range.  I am looking for a similar A/D that samples really well to use as a
192kHz converter, for a lower-end solution similar to the Janus/Ozy
combination.  I want to use this with a USB interface for laptop SDR
applications.  Someone has mentioned he is already working up a design with
similar design goals (from a couple of weeks ago),a nd I hope he finishes it
up.
Terry



----- Original Message ----- 
From: "Orval Chadsey" <n6ozi at earthlink.net>
Cc: <hpsdr at hpsdr.org>
Sent: Sunday, April 22, 2007 2:03 PM
Subject: Re: [hpsdr] sampling


> ***** High Performance Software Defined Radio Discussion List *****
>
> On Sun, 2007-04-22 at 11:00 -0700, Orval Chadsey wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > On Sat, 2007-04-21 at 23:25 -0700, Glenn Thomas wrote:
> > > ***** High Performance Software Defined Radio Discussion List *****
> >
> > > I don't know why 192 KHz.
> > >
> >
> >
> > Simple...
> >
> > 44.1 KHz X 4 = 88.2 KHz
> >
> > 88.2 KHZ X 2 = 192.4 KHz
> >
> >
> > 73 de N6OZI
> > Orval
> > San Francisco, CA
> >
>
>
> Oh shoot! So much for my arithmetic!
>
> Orval
>
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