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Re: [linrad] Re: Presonus Firebox Help Needed!!

Thanks for the note, Leif!

I have emailed Presonus to see what they say.  I will let you know ;)

The new webpage is very interesting...and it must have taken a long time to do all of that testing. Since people have different systems, I am sure the information there will be very helpful!

I have to work early tomorrow, so I will have to stop now.

Have a great week, and



On Sun, 28 May 2006 18:30:25 -0400, Leif Asbrink <leif@xxxxxxxxxx> wrote:

Hi Roger and All,

This is another post regarding problems I am
seeing with the Presonus Firebox. I am hoping
for one of the I/Q gurus to help me figure out
what is going on.  My questions are basically:

1.  What is happening?
2.  Is it a hardware or software problem?
3.  Is this behaviour present in all Fireboxes,
in which case I will keep it, or is it unique
to mine in which case I will send it to the
manufacturer under warranty.

I am seeing MAJOR problems with the I/Q signals
sent by the Firebox over the Firewire to the
computer when it is operated at 96kHz sampling
rate. These problems are not present at 48 kHz
sampling rate,
The malfunction is this:

There are identical spectra displayed above and below the center
frequency.  I used the signal from CHU at 7.335 MHz as my 'signal
generator' for these tests, as all of my test equipment is at a remote
site. The CHU signal can be detected between the center frequency and up
to 23000 Hz above or below center frequency, but not beyond [i.e., the
bandwidth over which an input signal can be detected is about 48 kHz or
half the sampling rate, just as if the card were running at 48 kHz
You hit the nail on the head:-)

I added a 19th figure on this page:

I had seen something similar - but four signals rather than two
when trying Windows 98 on a slow computer.
After upgrading the drive routines I save exactly what you

The sampling happens at 48 kHz and a VERY simple routine is
used to up-sample. You can see the same it you set the Delta 44
sampling speed to 192 kHz in ALSA.....

As far as I can recall, OSS has a filter that removes most of
the false signal if you use it for up-sampling.

But there is noisefloor displayed
over the full 96000 bandwidth of Linrad or Winrad, and the CHU signal will be displayed over the full 96000 bandwidth as one varies the LO frequency due to the 'extra' signal appearing on the other side of the spectrum from
the real signal, as is shown below.
Yes. The upsampling creates a spur every 48 kHz and one of them is
always visible (including its noise floor) - but not if you use OSS;-)

I suggest you write a complaint to the manufacturer. You bought
something that was said to sample at 96 kHz - but it does not.
The hardware is most probably fully capable (at least the digital
stuff - there could be an analog low pass filter somewhere but not
very likely) Try to force the to give you new firmware/ drive
routines. The A/D converter is presumably sampling at something like
64*96 kHz and it should just be instructed to down-sample one step
less. (Why not ask for 192 kHz if you get into a dialog with the
right people. They might get many additional customers.....)

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Roger Rehr