Originally Posted by tomelex
I agree with the idea of recording from the phono output, and while I think I have read all these pages in this thread, I do want to remind that cartridges have spikes and spurious outputs (passed on by the phono amps) well out to 30khz and more. There are also low frequency anomalies (but digital handles those no problem), so just saying that those spurious high frequency signals if passed through a digital device with a steep filter will then not pass on to the rest of the analog chain, and henceforth there will be less IMD effects, so the broader the frequency range of the digital the better IMO for this test. Those HF signals can IMD back into the audio band and that may be audible depending on their amplitude etc. just sayin incase we have not thought that through.
Also, an astute listener will be able to hear the different noises from each replay of the LP, since LP sounds different each time it is played, so that is also a bit of a trouble spot in this test, LP NEVER plays the exact output each time.
Also, when you que into or end a song, the lp will have different noises in those quiet areas too, so that is another thing to consider due to the variability of LP playback.
Years ago when we did home made a/b testing, we use the preamp output to record from so folks did not hear the lead in and out of the songs, ie you bring up the volume a few seconds into the song and close it down a few seconds before the song ends, this was when we strictly used LP as our source only, because the lead in and out never sounded the same due to the groove noise.
Anyway, the more precautions you take the better for this test to have validity. The reason the losing side will give for results not as they expected was the system was not transparent or revealing enough, despite your process looks good enough to me, just sayin.