Room correction with REW without a calibrated mic?

[hjf]

I ordered a UMIK-1 which should arrive in a couple of weeks. Meanwhile I'd like to experiment with REW, with a DCX2496 I got second hand.

As far as microphones go, I have an Audio Technica AT-2020 (XLR through a Zoom H4n Pro), and a Rode Podcaster (USB). Can I use these to experiment while the proper mic arrives or will it be a waste of time?

 

[AllenB]

Things were OK before average measurement mics were getting calibrated.. good systems were produced. Getting a USB mic might be a bigger problem if you want to do crossover work.

 

[jan.didden]

Can I hitch onto that? I have been in a discussion whether you'd want to use a USB mic like the miniDSP UMIK series or an analog mike with REW.

The reasoning was that the USB mike A/D and USB sampling/timing is not sync'ed with the D/A timing of the measurement signal sent out to the system under test via a soundcard.
If you would use a soundcard with an analog mic input, the signals to/from the PC would be sync'ed internally in the soundcard.
The thesis was that if the signals were unsync'ed as with the USB mike, the measurement would be inaccurate at some level.

Anyone can shed some light on this?

Jan

 

[AllenB]

Yes, the main problem is getting the delay right between separate measurements. To explain this there is a workaround for USB mics that adds a timing reference signal. The additional reference speaker has to be held at a fixed distance from the mic between measurements.

 

[jan.didden]

Interesting, thanks Allen. I hadn't heard about this at all, but Acourate strongly recommends an analog mike for this reason.
Do you have a link to a workaround?

Jan

 

[AllenB]

It's the acoustic timing reference that has been built into REW.

 

[ctrlx]

here are the two extreme curves from ten small eletret mic capsules i tested

in this capsules case, if your working below 4-5KHz it should be resonable flat, above that response can vary

 

[jan.didden]

@ctrlx, how is this related to timing issues?
I guess these are analog mics?

Jan

 

[WhiteDragon]

Analog gets turned into digital at some point.

Its up to the software to sync clocks.
And up to software to delay input/ output based
on latency of system.

Full duplex be more useful
either way, will be delay

 

[jan.didden]

Then the next question becomes, does software like REW, where a digital mic is recommended, take care of the re-sync or delay compensation?
Anybody knows?

Jan

 

[brig001]

Yes it does. I use it over AirPlay which has a 2 second delay to the speakers, and it works fine

Brian

 

[ctrlx]

@ctrlx, how is this related to timing issues

Jan

err, its not.
it is related to the thread title and post 1.
may be a mod can add "OP," to my post.