On Wed, Aug 10, 2011 at 9:49 PM, Oli Glaser wrote= : > Hmm, the highest level there is around -60dBu (at a low frequency ~200Hz > so unlikely to be the high frequency noise you are hearing), and most is > under -80dBu which I wouldn't call significant noise. 0dBu is 0.775V > RMS, so -80dBu is 0.0000775V. > Have you tested the signal before it goes into the box you bought? Can > you describe your audio chain in detail so we can get a good idea of > what you are doing and why you think the box is causing the problem? > I did not test the signal going into the box. But I do know that when I plu= g the guitar into the dedicated amp, there is no noise at all (very little 60Hz noise, and nothing other than that). The setup I have is this: guitar (analog signal from pickups) -> guitar link box -> computer (via USB= ) -> various software that was tested produced the same noise (Guitar Rig, Garage Band) headphones or mini stereo system (via regular analog stereo headphone cable= ) <- guitar link box <- computer <- software When exactly does the noise turn up? As soon as you plug the guitar in? > The noise is there regardless of if anything is plugged into the guitar interface box or not. Plugging the guitar and/or headphones in and out does not really change the level of noise that much. When you turn a certain effect/amp on? If it doesn't happen on a clean > sound then maybe it's either intentional (e.g part of the intended > character of an old amp sound) Good question. It is still there on the clean setting (no particular amp or effect selected), but it is very low intensity and I have to turn the software input gain up to hear it. It is still there though. However, when a particular amp/distortion pedal is selected, the noise becomes much more prominent. I think that the distortion pedals are somehow amplifying the noise (perhaps by boosting the treble). > or some issue with the > processing/drivers? I saw on the link that someone suggested using the > Behringer Guitar Link UCG102 drivers instead: > http://club.dealextreme.com/forums/Forums.dx/threadid.579785 > It doesn't matter which drivers I use. The ASIO4All drivers are far superio= r anyway. MUCH lower latency. Exact same issue on my Macbook Pro laptop. Same symptoms and behavior. The drivers on the Mac are "built in" by Apple I assume. To find out where the noise is coming from you need to make it happen, > then follow the signal chain right from the start to see where the > unwanted accentuation/distortion appears. Some white noise at the input > during this might be useful to see what is happening to all frequencies > easily - whatever the input is it needs to be reliable and a known > quantity (i.e. not suddenly likely to burst into high end distortion). > If you narrow down a likely culprit, then we can try and figure out what > is causing it, but I would first try and confirm beyond reasonable doubt > it's actually the box causing the problem. > I'm /pretty sure/ it is the box, but I could be wrong. My dedicated amp and distortion don't have any noise other than the 60Hz which becomes much more prominent when I touch something like a 60Hz power line. I suspect that it will have a cheap opamp in there as RR suggested, and > I agree (if it's actually causing a significant problem) swapping it would be an easy way to improve performance. > Could it also be the ADC? > If you want to build your own I'd be prepared to spend some time and > effort on it. If the goal is just to get a decent guitar recording setup > I'd say forget it and stick with that (or make a simple improvement like > swapping the opamp) or buy another better one. If you want to increase > your understanding of audio/USB/DSP then go for it, I'm sure you will > learn plenty. > Yes, I would also like to increase my understanding of those things. I'll work on it slowly as I get time I guess. Unfortunately, I don't have a good spectrum analyzer to pinpoint the noise. And it's hard to prototype an opamp setup when all the good ones are SSOP and stuff. I just have to design it using LTSPICE/DipTrace and hope I'm doing it right and send in the board for fabrication. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .