Basic acoustic measurement primer v3.0

[soundgou]

where I can find the primer v2.1, I try to find a link but I can't

please help me

[DanDan]

You are in the thread, go to the first page top if you can. There may be a problem with links within GS. Another one failed elsewhere yesterday.
Here's what you asked for anyway, hope it works.
http://www.gearslutz.com/board/studi...er-v2-1-a.html
DD

[Chris_Nicks]

Hi dandan or anybody. question about measuring. Ive hardly heard anybody mention about the speaker used in measuring. How important is it to use a very flat studio monitor versus a cheap Hi-Fi/desktop speakers? will the use of the cheap desktop speaker not give accurate results as to room measurements?

[aackthpt]

Originally Posted by Chris_Nicks

Hi dandan or anybody. question about measuring. Ive hardly heard anybody mention about the speaker used in measuring. How important is it to use a very flat studio monitor versus a cheap Hi-Fi/desktop speakers? will the use of the cheap desktop speaker not give accurate results as to room measurements?

Firstly, most speakers are going to be very flat compared to most rooms, so the speaker is usually not the most important factor. Secondly, the speaker and room are a system - you don't listen to only the room, you listen to the speakers in the room. Therefore you test the speakers and the room together, and when you change something (like speakers) you should remeasure the system.

If you want to comparatively test speakers independent of a room, you need to use different procedures that are not detailed in this thread.

[hereticskeptic]

I'm getting pop-up messages/error messages every time I try to measure using REW. Is there any chance someone would be willing to help me troubleshoot what I might be doing wrong? I have a graph, but have no idea if it has been done properly, and REW certainly doesn't seem to think so.

I currently have a 75dB SPL reading at the mic's position, which is exactly where my head would be, at the exact height my ears would be. The mic is pointing at the left monitor. What else needs to be done/checked before a proper reading can be measured? Thanks in advance.

[DanDan]

Apart from the fairly steep learning curve, there are issues.
REW doesn't work with multichannel interfaces on Mac computers.
If you have a Mac and anything other than a simple stereo interface, omit that I/O and use the onboard Line In and Out. They are of decent quality.
So heretic, are you on a Mac? What does the error message say? A screengrab or snapshot AppleShift3 perhaps.
DD

[hereticskeptic]

Originally Posted by DanDan

Apart from the fairly steep learning curve, there are issues.
REW doesn't work with multichannel interfaces on Mac computers.
If you have a Mac and anything other than a simple stereo interface, omit that I/O and use the onboard Line In and Out. They are of decent quality.
So heretic, are you on a Mac? What does the error message say? A screengrab or snapshot AppleShift3 perhaps.
DD

Oh okay. Yeah, I am using a Mac and a Metric Halo ULN-2 interface, which has digital i/o, but only two analog input channels and 4 analog output channels. Will this work, or should I use Fuzz Measure to avoid issues? The error messages have been different, but I've attached a screen shot of the current one. Thanks for the reply DanDan!

[hereticskeptic]

Here's a response graph I just took where two different messages popped up. The second of the two messages is the same as in my prior post, but this time it followed the first message in this post, after selecting "OK" for the first message. In other words, even when my input volume level is above -10dbFS, I'm still not meeting the requirements to get a suitable impulse peak response. The input volume goes above -10dBFS when I turn the interface preamp gain up, but I still get that impulse peak error message.

[DanDan]

You are welcome. The 4 outs probably qualifies the interface as multichannel. The fault lies with Apple not doing Java correctly for multi. I had a lovely Lexicon iONIX which I found unusable. The same error message about the IR peak not being in the right place. But more importantly weird unusable readings. I believe you can use the Output of such interfaces, which saves some wiring, monitor controllers etc. However, the inputs will be unusable. Use the onboard Mac Line Input and an external Mic pre. If there is a H/W insert on your interface you could use this as a Direct Out.
Persist, REW is very very good.

DD

[hereticskeptic]

I did a bunch of measurements in FuzzMeasure, and am pretty sure I got that working fine. I shut the cpu down for the day, but could post those if that's cool. Should I just upload jpeg files, or something else?

[DanDan]

FM is pure Mac, works every time. You can export the IR and then examine them in REW using it's (superior) tools.
If the file is not too big, you could Zip it and post it here.
However, this thread is long. Unless there is a measurement anomaly or detail of interest please PM or email me via the direct email on my website,, with queries about the measurement.
I will happily help you personally.
DD

[audionerve]

This was a damn good read. Thanks for writing all that down!

[milosh_]

great article

thanks !!

[brimstone]

give thanks dan, awesome stuff..

am just going into studio today to do a test for my studies and when I read through this a couple of weeks back it was most beneficial.. any ideas when you will have v3 ready as I anticipate your excellence in this field..

[hally]

[pitchfork]

Hi DD. Thanks so much for posting V.3. Now I understand what you mean by...PRIMER...DOH!

Ok, I do have a question. Like I said, I've purchased a measurement mic. Not the best in the world, but according to Ethan, it'll work...at least for us HR guys. However, it'll be a week before it gets here, and I'd sure like to try this REW stuff out. I have a Rode NT2 large condenser, with an Omni switch. Will this work? Thanks.

Oh, does the room have to be empty. I have a ton of audio gear(4 R2R, console, consumer playback gear etc..in racks.

Oh, another one. Should I use the speakers in the soffets, or the nearfields on my console?

[DanDan]

Rode will be fine in Omni. Room as it is or will be is best. Drive just one speaker as described, then the other, then both if you wish. I will get into that and other detail as time goes by. In the meantime it is good to become familiar with driving the software.
It gets easier.

DD

[offthewallstudio]

thanks for the post! Were can i download this program to mesure my audio IR?

[DanDan]

REW REW - Room EQ Wizard Home Page
FuzzMeasure FuzzMeasure Pro 3
ARTA ARTA Home

[DanDan]

A confusing Topic which keeps coming up. Similar to the Two speakers thing.
We see recommendations on websites to point the mic upwards and to drive both speakers.
Both are valid, but only in exceptional contexts.
It is normal to point a Free Field mic at the source of interest. Dual sources can be very confusing, especially when reflections are being considered.

Most of the common measurement mics are Free (Direct) Field. They are at their best pointed Directly at the object of interest.

The Cal File which comes free with each individual Dayton EMM6 corrects (calibrates) the response to flat when the mic is used On Axis in a Free/Direct/Near Field.
EDIT, it appears they now supply three Cal files 0/45/90 degrees. How perfect.
Similarly the UMIK-1 from MiniDSP comes with a Cal file specific to the actual mic supplied.
Given the small price of either of these, it really does not get any better than this.

The generic Cal Files for the ECM8000 at REW try to do the same job using a generic response averaged over several actual mics.
Home Theater Forum and Systems - HomeTheaterShack.com
These generalised files clearly cannot deal with individual mic variations which are far from the average.


The Dayton and MiniDSP are clearly better choices.

The most accurate response for the UMIK and the Dayton (using the 0 degree Cal file) will be Mic horizontal, pointing at the area of source of most interest.
The Dayton has the advantage that you can point it upwards to hear the rooms and speakers more equally (e.g. for 5.1) but still get decently flat response by using the 90 Degree Cal File.

Exceptional Circumstances
For simple L/R or Surround Level balance, it is convenient to point up (or down if carpeted). This will (mis) treat all incoming horizontal HF equally. Pink Noise and an SLM are also convenient for this work. REW provides these.

Mics in USA ANSI standard SLMs are designed for Diffuse Field. There are very few standalone Diffuse Field measuring mics. When using a Diffuse Field mic, follow the instructions, point it upwards, perhaps leaning towards the source, e.g. 70-80 degrees.

Confusingly, the FR graphs seen in advertising for the ECM8000 suggest that it should be quite flat up to 10K when pointed upwards.
The problem with this mic is the differences seen between individual mics, as seen in the above HTS link.
EDIT A GS has recently tested an 'original' vs a new ECM. The new one has a very wild response.

DD

[mistergreen]

Is anyone using REW on a standalone (no internet) PC? I am having trouble installing it. It keeps trying to connect to the internet to look for JRE. I removed JRE7 and installed JRE6 with no success.

[Rod Gervais]

I use it without connection to the internet.... have never had an issue...

Rod

[Rod Gervais]

I use it without connection to the internet.... have never had an issue...

Rod