From G3PLX:
Lee:
Yes, this is what I have discovered the hard way. I was naively expecting
the new 24-bit device to be 8 bits better than my old 16-bit card, but I
have learnt that it isn't that simple.
But this latest discovery is not just about specmanship. There's something
odd going on
From G3PLX:
Gerald: Thanks for your response with comments on 1/f noise and image
balance.
I am really not convinced that 1/f noise is 'physics' in the same sense as,
for example, thermal noise is physics which we can't fight. Some circuits
exhibit what we term 1/f noise and others don't seem
From G3PLX:
Jack said:
If the cable isn't to blame and this is DDS tuning - as Eric seems to
suggest - then perhaps Peter's comments on linear tuning of the
AD9854 hold an answer. But if DDS tuning is the cause, why is it
frequency dependent?
DDS tuning clicks should ONLY occur if there's a big
From G3PLX:
From what Ahti says, there is not a 1/f problem with the current SDR1000,
which is what I found with the earlier version, but the oscillator radiation
effect may or may not still be there.
In the last topic I raised, concerning 24 bit soundcards, I speculated that
the 'ideal' ADC
From G3PLX:
Alberto:
Thanks for your input! The peak in the centre of the spectrum plot you
showed at http://sundry.i2phd.com/zeropeak.gif is certainly the small DC
offset of the ADC's in the Delta 44. The Zero-IF software would remove this
of course. It can be done automatically, it doesn't
From G3PLX:
The software that comes with the SDR1000 uses an 11.025kHz intermediate
frequency. I understand the reasons for doing it this way, but even before
the SDR1000 appeared I was doing software radio with an I.F. of zero. By
this I mean that the sine and cosine RF oscillators were set
From G3PLX:
I just checked my two soundcards for the low-frequency roll-off. My new
Firebox is 2.4dB down at 1.8Hz and the MP3+ is 1.5dB down at 1.2Hz. And that
was done quickly by linking line-out to line-in, so it includes the LF
roll-off of the transmit side too. I am quite certain the
From G3PLX:
Alberto: Thanks! That's the information I was seeking. It looks as if I
was half-right, if there are, at best, 18 good bits in a 24-bit card. As
Phil says, if 16-bit cards turn out to be worse that 16-bits, then there is
some reason to go for a 24-bit card (which is worse than
From G3PLX:
Chris: I wondered about dithering. If I understand the idea, they introduce
some deliberate noise in the ANALOGUE part of the ADC in order to spread the
spectrum of any quantisation noise. Without it, I can imagine a tiny
sinewave input of, say, one bit amplitude, looking to the
From G3PLX:
Thanks Paul. Thank goodness I am not alone!
I just did a simple calculation. The ultimate rock-bottom noise power is
kTB, where k is Boltzmann's constant (1.38e-23), T is room temperature (300
degrees K) and B is the bandwidth in which you measure it - let's say 24kHz
for a 48kHz
From G3PLX:
Sami is right. You CAN recover a signal from noise by narrowing the
bandwidth, so if my signal was level with the noise in 24kHz bandwidth, I
could filter it to a narrower bandwidth (in software) and improve it's SNR.
But that's true regardless of the number of bits in the raw
From G3PLX:
I am just starting to do some serious tests with my new 24-bit Firebox. With
the audio input of a channel short-circuit, if I analyse the statistics of
the 24-bit data, I find the bottom 8 bits are ALWAYS random. In fact the
bottom 9-10 bits are random.
This tells me there is no
From G3PLX:
Thanks for the pointer Phil. I guess hpsdr.org might be an interesting place
to browse anyway, but maybe I didn't make my point clear. I am not
complaining that the Firebox I have is NBG, I am wondering if anyone has
done any tests which establish whether 24 bit audio gives a
From G3PLX:
Alan K2WS demonstrated the horrendous broadband noise coming from a very
expensive Audigy 2ZS card by using the spectrum display of his IC-7800
http://www.n9vv.com/K2WS.html He dumped the Audigy and bought a nice
Delta-66 that has continued to delivery great performance and a
From G3PLX:
I don't know if this is common knowledge, but I found a major problem with
some soundcards, especially when running SDR software where the input and
output sides are running simultaneously.
I discovered (the hard way) that you cannot assume that if you set a card to
a given
From G3PLX:
Alberto:
Thanks for your answer (and pleased to meet you here). I have not heard of
'WMME' so that's another new word I must throw at Google and learn more.
However, if it IS just an extension of the old mmsystem API, then maybe it
still suffers from the terrible
From G3PLX:
Greetings to the group. Can anyone here help me with some questions in the
art of driving the Presonus Firebox?
The background is that I have been given a Firebox as an unsolicited gift.
All the DSP/SDR software I have written has been for 16-bit soundcards, and
I found the
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