12th May 2009
member no 666
Joined: Jun 2002
Location: Suffern, NY
Originally Posted by monomer
Well, i just sampled my laptops internal soundcard through my mackie 1640 while generating a sine (with the same machine).
There must have been at least 4 amps involved in the chain.
Sampled close to 0db @ 44100/16.
Freq: 441hz (to make aligning the waves as good as possible)
Visualy the top and bottom looked identical, but i spotted some randomness when looking at multiple cycles zoomed out over a longer period
After recording i realigned two copies of the recording so that it would sum to null, then i mixed them together.
The results are not realy surprising to me.
The 441Hz wave nulled beyond recognition.
At around -42db the first background noise started to appear.
Ugly spiky signal, but no detectable periodicity.
Also, and i know this from other measurements, it is typical bg noise of this laptops internal soundcard.
Spectral analisys showed no frequency at all present at 441Hz, tho enough dirt at other freqs.
A DC removal on the leftover dirt showed no difference visualy (zoomed in to around -50db peak).
So i realy dont think there is such a huge issue with amps and phase reversal / asymmetry.
Are we talking about the same amps?
What amps did you measure in your tests (more like, what was their purpose) ?
Flawed test. Check it out on an analog oscilloscope and you'll see what I'm talking about.
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