Richard,
You refer to various dB levels, i.e. you say that the plot you show is with an input of "-3dB". What is that with reference to, are you talking about dBu, dBV, or something else? Since a decibel is a relative measurement it is always with reference to some level.
It definitely looks like the Edirol is beginning to clip - I wonder if the front end is designed with a different max level than your MD recorder? What do the specs on the 2 devices claim for max input levels?
-Keith
When I say 0dB and so on, it is with respect to the UA5 *digital output*. So, to get -3dB, I just a moderate signal into line in (from a NJB3 line out BTW), and turn the trim pot on the back of the UA5 until the signal coming out is at -3dB. That is all. So, I'm not saying anything about actual analog levels here.
Note: I get problems with both mic and line in, so it must be something at, or near the ADC...
Richard
OK, I'm going to reply to my own post here...
After talking with some people who know more than me, the conclusion is, that for cheap ADC at least, you shoud *not* run near 0dB. Common sense would say get more signal and less noise, but it appears this ADC works best at say -6dB. I'm not sure how to do this at shows though. The CLIP light comes on at -3dB. I guess you should get the clip light and then back off.
Just to reiterate, I observed secondary peaks at -40dB when the input signal was at full scale. This is 1% distortion! So, even if you run at -6 or even -12 and boost in post, you're going to do better than that. Now that is distortion at the peaks only, but distortion none the less.
Now I don't know how other ADC's compare, but I do know that my MD has no such distortion at full scale! The amps might not be as good, but the ADC seems alright. I'm going to try my NJB3 line input as well.
I guess the moto is: trust your ears, but also run some tests!
Richard