Trouble getting started...

[brucek]

I'm sure I could correct this problem if I could find a way to eliminate these dropouts during the 1kHz test tone.

Yeah, I agree. Is your PC an older model that maybe can't keep its attention to the USB port?

I see in your manual they talk about performance:

Do not run other applications. You will probably use your computer for applications other than audio, but we recommend that you avoid running other applications at the same time you are running audio programs. Processing digital audio places a considerable load on your computer.
This means that if you are running other applications (especially graphics or Internet tools) at the same time as your audio application, the processing may not happen fast enough.
Certain devices such as network cards or WinModems can cause conflicts with USB processing. If you experience such a conflict, you can use the Device Manager to temporarily disable the offending device.
If your computer has an IDE hard disk, enabling Direct Memory Addressing (DMA) will improve performance. In Windows XP, this is enabled by default..

I have no problem on my laptop with VISTA and a USB external soundcard and REW. It doesn't seem that it is a very common problem, or others would have complained of this. Something must be running in the background. Hopefully you can track down the culprit.

I'm going to move this thread to the REW forum section to perhaps get more play...

brucek

I think I found the problem.

By trial and error mostly, I set the latency of the Tascam soundcard to the highest setting. The clicks/dropouts don't stop completely, but they're now down to about one every twenty seconds or so. Anyway, good enough to finally get a 'clean' soundcard cal measurement...I think !





The laptop I'm using is not all that old - 3 years - I think it should be fine for this application, especially now that I've turned off all unnecessary background applications.

[brucek]

Yep, that looks really good......... save it, and take a measure of the loopback cable with that soundcard cal file loaded (be sure to not have the SPL meter cal file loaded yet).

The result should be a flat line. Now that you'll be measuring, you'll use vertical scale of 45dB-105dB....

Then remove the loopback and hook up the SPL meter and receiver for real measuring...



brucek

brucek wrote:

Yep, that looks really good......... save it, and take a measure of the loopback cable with that soundcard cal file loaded (be sure to not have the SPL meter cal file loaded yet).

The result should be a flat line. Now that you'll be measuring, you'll use vertical scale of 45dB-105dB....


brucek

Here it is...



Can you help me understand the difference between the flat line at 110.1dB and the corrected and target curves down at 75dB ?

[HionHiFi]

brucek wrote:

Yep, that looks really good......... save it, and take a measure of the loopback cable with that soundcard cal file loaded (be sure to not have the SPL meter cal file loaded yet).

The result should be a flat line. Now that you'll be measuring, you'll use vertical scale of 45dB-105dB....

Then remove the loopback and hook up the SPL meter and receiver for real measuring...



brucek

Thats what I did to resolve the problem. That and copy the setting from your soundcard cal post. I haven't got back around to remeasuring with Audyessy engaged, maybe this weekend. Excited to see what the results will be.

At any rate, tickertape, now that your setup, and ready to go, what is your goal? What are you trying to achieve by using REW, and BFD.

[brucek]

Can you help me understand the difference between the flat line at 110.1dB and the corrected and target curves down at 75dB ?

The flat line at 110db is excellent and tells you that you have a calibrated signal. The only "mistake" you made was to not run the Calibrate SPL routine when you measured the cable and set it to 75dB. This aligns REW's SPL meter with the real world normally, but when running the loopback measure simply tells REW that the level is 75dB and to place it on the graph at 75dB..... no big deal, it doesn't matter that REW placed it at 110dB (it had no reference as to where it should place it). The important thing is that it is flat, which is what you would expect a cable to measure from 0Hz to 20KHz if you had a perfect soundcard (which you now have with the cal file in place).

Anyway, as I said before...you now will set your vertical scale to 45dB-105dB for all future measurements.

The target curve is what you want your sub only measure to track to, as long as you match the crossover frequency in REW to your receivers crossover frequency. It's a guide, that REW will use to evaluate the response of a sub and recommend filters for an equalizer.

When you are ready to measure, start with the mains in your system shut off and your receiver in stereo mode and the crossover set, so you will only have the sub playing.
Use a horizontal scale of 15hz-200hz for REW.

brucek

intelonetwo wrote:

At any rate, tickertape, now that your setup, and ready to go, what is your goal? What are you trying to achieve by using REW, and BFD.

I still haven't figured out what BFD is, but I ultimately plan on calibrating my home studio, and my home theater. And since I have an on-location mobil studio, I'll probably calibrate and do some limited room treatment to various performance venues now and then.

What is BFD ? ...lots of acronyms out there ! ...reminds me of the military.

[brucek]

It's an inexpensive parametric equalizer that a lot of people here use to equalize their subwoofers.

REW will recommend filters to enter directly into a BFD. In fact you can connect a midi /USB cable from your PC and download the REW recommended filters into the BFD (or you can enter them by hand).

BFD stands for Behringer Feedback Destroyer. No-one uses the feedback destroyer function of the BFD (which eliminates microphone feedback on a stage for musicians), but we use the two channels of 12 parametric filters that happen to also be a feature of this unit.

REW will create suggested filters for several equalizer types besides the BFD. The filters are what that target line is all about that you questioned....

We have a BFD Guide to get you started...

Not everyone requires an equalizer, as speaker placement and treatment are the first order, but if you have a large resonant peak at sub frequencies, it's hard to beat a cheap BFD.

First you have to take measurements of your sub from the listening position......... that's what the goal of this journey is all about.......

brucek

Brucek,
Thanks for that explanation (about BFD).

Everything seems to be working correctly now, thanks to all your help.

Now, is there anything I should know about transitioning from SPL measurements to measuring with a reference microphone ? (I do have a calibration file for the microphone) The "Making Measurements" section of the help file seems to discuss taking measurements only with the SPL meter.

[brucek]

Now, is there anything I should know about transitioning from SPL measurements to measuring with a reference microphone ? (I do have a calibration file for the microphone) The "Making Measurements" section of the help file seems to discuss taking measurements only with the SPL meter.

Yeah, you'll still require the SPL meter for a one time hand held refernce during the Check Levels routine, when you use a microphone.

Here's the deal...

You connect the microphone (and its preamp, or connected directly to a mic input of soundcard with built-in preamp). Then you connect the line-out to your receiver (always in stereo mode with all soundfields and effects off) and the crossover set to the normal one you use (i.e. 80Hz).

Be sure the soundcard cal and the microphone cal file is loaded into REW.

Run the Check Levels routine and set the output sweep level of REW to -12db, and then adjust your receiver volume so the level at the listening position is 75dBSPL. This where you hold the Radio Shack SPL meter near your hooked up microphone so you're able to set that 75dB level (kinda hard without it). Once that's done, put away the SPL meter.

Now set the REW line-input level until it's at ~-12dB. The levels are now setup - finish....

Then run the Calibrate SPL routine in REW and set it to 75dB (now the REW meter knows what 75dB actually is).

Now run the Measure routine.....

brucek