I've used a Sony ECM 44B for interviews for several years now. While no client has ever complained, I thought the sound was just a little muddy.

So I took my Z1 into an audio supplier to do an A/B comparison between a Sanken COS11 with the Sony. I recorded HDV (my usual format these days) so the sound was mpeg layer II. I captured Cineform intermediate and played created a take for each channel so I do an A/B switch on the same material.

I was surprised that I could not hear a difference in the sound quality between the two mics. The only difference was that in recording, I had to set the Z1 level control to 9 on the 44B's channel to match the Sanken set at 4. I would have thought this would have meant I would hear mic preamp noise from the Sony during quiet points in the taping. Not so.

I couldn't tell the difference between the two. And yes, both sounded just a little muddy to my ears.

I'm thinking it must be one or more of the following:
1) the camera's preamps aren't good enough to reveal the differences
2) the MPEG layer II format somehow strips out the differences
3) capturing to Cineform intermediate strips out the differences
4) my 55 year old ears are getting muddy
5) there isn't much difference in the sound from lav mics properly placed on the subject.

Any experience/thoughts?

Try the test again, but this time record in DV mode instead of HDV mode. The audio in DV is supposed to be noticeably cleaner, according to Oleg K., than the audio in HDV mode.

That'll remove one variable (MPEG-1 Layer II compression) from your test. It'll let you hear the mics more directly.

If it turns out that you can hear a difference when in DV mode, but not in HDV mode, then that'll answer whether the compression is causing you to not be able to hear the difference. And then, if the ultimate goal is to record on the Z1 in HDV mode anyway, then you'll at least know that moving up to the better mic isn't likely to actually gain you any benefit in the final product, right?

To my ears the Sanken COS-11 is worlds better than the Sony. I only use Sankens, but have a few other types for risky situations. FWIW it was Peter Jennings mic of choice as well as scores of motion picture sound recordists. They are delicate and can not be rewired if they fail at the capsule although there is a trade in program for a new one ($265).

If you know a good voice over studio you can compare in a top notch sound room.