Afro88
Joined: Jun 20, 2004
Posts: 701
Location: Brisbane, Australia
Audio files: 12
G2 patch files: 79
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 Posted: Fri Oct 08, 2004 5:52 pm Post subject:
G2 input noise |
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[This is a continuation of the discussion on input noise started in the sleeping G2 thread http://electro-music.com/forum/topic-3737.html]
| Quote: | | Fozzie: The gain in BH's patch is 4096x, so imho opinion it isn't that strange that you pickup something there. Maybe the new G2 converters are even better at being a random source than the classic ones with fewer bits. I reckon that, even as they have a better s/n ratio, the noise floor noise might actually be more random noise (better noise? is there such a thing?) but with more 'real signal headroom' above it. I guess the first couple of bits in a 24 bit AD conv are more sensitive to be affected by anything than the AD conv's with lower bit specs. Or is this pure nonsense? |
| Quote: | Blue Hell: To pick up something, yes. But 4096 amounts to about 36 dB and I get an output signal that almost hits the clip level, something I did not quite expect.
The measurement should have been done with inputs connected to some impedance, which would have given less noise probably. I remember having done this experiment with the NM classic as well, and that one was not very suitable as a noise generator.
It's not that input noise had been bothering me, but the numbers surprised me a bit.
Jan. |
| Quote: | Fozzie: Jan, I had also calculated the 36 dB value after I posted my previous message, and wondered whether I had done something wrong or missed something. Indeed, that doesn't sound good. However, plugging in my bass (I do that a lot) after the preamp stage works better in the G2 than in my old MM, as I don't hear any obviously added noise (either of them), but I do have far more headroom before the input clips in my G2.
A bit OT: there is one thing I seem to notice about the AD's and DA's on the G2. If I run my bass through the engine, with no processing other than in/out and some mixer things, the signal seems to be brighter than origal. Possibly a bit less 'deep lows'. Anyone notice this too? |
Hmmmm... Do you guys have anything connected to the inputs? If I use BlueHell's patch, I have to turn down the white noise amp to 1.19x to be at the same level (meter wise) as the gained noise from the inputs.
Also, I read that 36dB value and thought there's no way that can be true, so I rigged up a mixer set to dB after the gains and played around with it's level. It seems -72dB matches the untouched input level.
But with my G2 engine I can actually gain the noise higher without it clipping. A further 2.14x gain brings the level up to just below clipping, and attaching a mixer set to dB at the end and attenuating the signal by -99dB results in the noise level being slightly higher than the untouched input noise. 99dB signal to noise ratio sounds about right for 24bit converters yeah? (unless I've missed something blatently obvious...)
Attached is the patch demonstrating this. Variation 1 shows the original gain structure from the previous patch, with the mixer attenuating the signal by 72dB. The switch changes between the gained/attenuated signal and the clean signal. Variation 2 shows the highest I can gain the inputs on my G2.
| Description: |
| Experiment with the noise levels on the G2's inputs |
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Download (listen) |
| Filename: |
noise2.pch2 |
| Filesize: |
1.22 KB |
| Downloaded: |
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blue hell
Site Admin
Joined: Apr 03, 2004
Posts: 24411
Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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| Posted: Sat Oct 09, 2004 4:56 am Post subject:
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Good idea to split this off.
No I did not have anything connected to the inputs (and said so, more or less, in one of my earlier mails - I should have connected some suitable resitor at least).
The figures you quote are much more like what I had expected, so maybe the conclusion has to be that the inputs have higher impedance than those of the Classic. And when left open they pick up signals from the environment, be it G2 internal or external.
I do have some cables running near the inputs, MIDI , USB, Audio and mains (but I hear no hum).
At the same time I'm sort of interested in this noise though, as maybe it can be used as a 'true' random source. I'd have to first find out what it's nature is then, of course. (Un?)fortunately I'm loaded with other projects currently ;-)
Jan. |
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