Frequency measurements with different inputs

[Divasson]

I think moving the speakers is only one possibly less important part, since youre not changing the room node/ echo characteristics.

Maybe the position of he mic in relation to 1) the room nodes 2) the speakers 3) the combined room & speaker reflections is the problem?

It should be easy enough to run a test
a) original placement
b) original placement with loads of wall damping, blankets hung from walls etc
that should tell you something

but to be honest, it looks like a hard reflection problem so I think you're stuck with first doing some room/furnishing treatment. (is it a boxy room/lots of reflective surfaces or is a room thats quite open-plan/ heavily damped ?)

the website I linked to suggests that this effect is linked to disruptive time delays etc. Since its a closed-loop system when performing REW measurements, I wonder if using different cable types is simply introducing different time delay at the speakers (due to different amp path), so REW sees a different time bias. We're only talking parts of a millisecond: This wouldn't affect sound-quality when listening normally, but might be important in a closed-loop test configuration where the software is both generating signals and simultaneously checking the response (the linked website shows there is a relationship between delay, distance, phase etc).

I have done another test, using a very sophisticated spectrum analyzer: my ears. I have run several times diverse frequency sweeps, very slow, from 800 to 2000 hz, covering the biggest through. When they say that 1dB is the smallest frequency variation a trained ear can hear, and that 10dB is like doubling the apparent loudness at middle frequencies*, I guess that i should be able to detect a 30dB variation!

Well, I can't hear any significant variation. So, it is not real. Then, it must be the test setup. What happens that does not happen with Toslink?

After thinking for a while: it may be related to the latency of each method, that may interfere with the readings. Toslink has the lowest lag - it is just a direct digital connection. Air, even with ethernet, has at least the minimum latency fixed in the settings screen: 50 ms. USB should have a short latency too - but it may be enough to trump the REW measuring logic.

And USB sounds so much better than Toslink with Audirvana 2.0.2. So, let's relax and enjoy.


*while doubling power is 3dB, and doubling voltage is 6dB, the apparent loudness seems to double with each 10dB