Simple set up :

you send the signal from your converter out, with state of the art cables, and you plug it in the same converter.

You try to null it with the original file.

So far, i have tried this with a lavry blue and an SSL converter.

I did not succeed.

One guy claims he has done this with an Sound blaster card.

Is this possible ?

And if not: Why ?

malice

Due to issues like the need for low-pass filtering and DC rejection, it may not be possible to get a "perfect match" at all frequencies when you "loop" a signal from a DA converter output to an AD converter input; even with the 1kHz levels perfectly matched. The low-pass filter effect would certainly be less of a problem with sample rates higher than 44.1 or 48 kHz.

Assuming you have already compensated for the time-delay by "sliding" the waveform in time to align the "loop" recording with the original (source) file, you may need to make subtle level adjustments within the recording software to one of the two files in order to perfectly match the level. This may also extend to inter-channel balance; so it may be necessary to adjust the level on each channel separately to get them both to null. Even then, you might not get a complete null due to differences resulting from the filters I mentioned (above) as well as a small difference in level due to the "step size" of the digital level control.

Also; if you do this with a 16 bit file there is a better chance of a (very nearly) complete null, as versus a 24 bit file, because the differences may be low enough in level to be obscured by dither and analog noise. It is possible the guy with the SoundBlaster card has too much noise in his monitor system or listening environment to hear the very low-level differences in his test.

Realistically, the only way to get a complete null is to compare two digital files that are "clones" (perfect digital copies).

Brad Johnson
Lavry Engineering Technical Support

Thanx a lot Brad,

This confirms totally what I suspected and my personal experiments

malice
(very happy Lavry Blue owner, btw )