REW for pro sound (interesting but long!)

[enovikoff]

Hello,

I'm investigating using the BFD for a pro-sound application. I'm the sound guy for a spiritual teacher who gives lectures and teaches meditation at a variety of venues. At each one, I have to ring out the system and EQ the room in order to make her speech intelligible. Currently, I'm using a Soundweb 9088ii (a fully-programmable general purpose 48-bit DSP unit which is set up by drawing schematics of filters, EQs, compressors, etc. - an audiophile's dream!) as an assortment of filters, compressors, auto-mixer, crossover, and remote-controllable mixing console. Then, I use a Sabine Feeback Exterminator to cut feedback (and add hum: grrr!). There's an output from the Soundweb to a computer for recording as well.

My current procedure for EQing the room involves using the Soundweb to generate white noise, read it into my sound capture software, analyze it with an FFT, turn the FFT analysis into a filter, invert the filter, and manually enter it into a 12-band parametric equalizer block that I designed into the output section of my Soundweb configuration. This is a lot of work, and visually inspecting the filter curves and turning them into parametric EQ definitions exceeds the average person's ability to do reliably. And then, after all that, I still have to make adjustments "by ear". The room EQ not only has to compensate for the bass resonances y'all like to talk about, but also for excessive brightness or dullness due to room design and furnishings. Even worse, the EQ changes when the room is full of people, but that's a discussion for another day.

There is a nifty Sabine product for automatically re-EQing your room as conditions change (the Real-Q2), based on sub-audible test tones placed into your audio program material, but after my experience with the Feeback Exterminators and the extreme hum and hiss they introduce (despite all balanced connections), I'm hesitant to buy another Sabine product!

So, I'd like to replace the Sabines with a FBD and use REW to set it up. Or even, just use REW with my current setup. However there are problems:

1) I don't want to have to set up output and input volumes each time I want to EQ a new room, or calibrate anything. I don't think this is necessary because I'm always using the same equipment and I can visually fix (with a volume control on the Soundweb) any low or high test tone levels so a measurement will be successful.
2) I don't really care about absolute dB levels. I'm looking at adding filters to cut (or boost - I have lots of headroom on the Soundweb since it runs at 48 bits) *relative* gain levels, so the absolute levels that REW seems to care so much about aren't really important to me. I tried a procedure where I used REW with no calibration (my Soundweb and MOTU sound card are essentially set up to be completely flat when I turn off all the PEQs), manually adjusting volume to get a successful automatic measurement. Then, I manually adjusted the target level in REW to be near the bottom of the average measured response, and then created filters as necessary. This seemed to work.
3) Since I want to equalize both for tone as well as resonance, I'd like some automatic help doing this. The automatic filter creation at low frequencies concentrates on peaks, which is fine. At higher frequencies, I want to level the average response first, then remove any big peaks or dips. I can do this manually by setting the averaging to 1 octave and adding some wide BW filters, then reducing the averaging window and adding more filters. Can this be done automatically? Or more precisely, is there any interest in doing so?
4) Being constrained to 12 filters (running out of CPU power on the Soundweb) is a problem, but then big rooms seem to have few bass resonance modes, so most of the filters are available for tone EQ. If I switch to a BFD, it looks like there are more than enough filters to solve any EQ problem though I could run out if I try to use it both for feedback and EQ. BUT again, figuring lots of PEQs out manually takes a lot of time. Then again, because of the small resolution (only 24 bits) I can't use PEQs to boost gain much, since I'll probably cause a math overflow or output clipping. On the Soundweb, error lights come on if you have a math overflow, and the location is shown in your schematic, so it's more bulletproof.

Does anyone have any comments on this? John, can you help me with some changes to REW to support tone EQ (even if it's just cuts and not boosts!)?

Thanks for listening and commenting!

-Eric Novikoff

[Wayne A. Pflughaupt]

Welcome to the Forum, Eric!

If I understand right, you’re using the BSS for room tuning and the Sabine for feedback control, and you want to replace the Sabine?

The BFD is pretty much universally panned by live sound professionals – not sure exactly why, but you’ll have no problem getting feedback about it from the Live Audio Board (no pun intended).

I’m not sure how well REW would work well for this, at least as far as the BFD is concerned. As you probably know, feedback is a combination of the speaker’s and the mic’s response. I suppose you can get the mic signal(s) fed to REW easy enough via the Soundweb, and probably do a MIDI connection to the BFD from it. But when REW is told to look for peaks, AFAIK it’s going to look for all peaks, not just the potential feedback peaks, and since you’re sweeping for full-range response, it’s going to use all 12 of the BFD’s filters – count on it. So you’d have to manually undo all the peaks not related to feedback. Perhaps John can comment further – I’m still getting my feet wet with REW.

Personally I just use an analog parametric for feedback control, ‘cause it’s quick and easy. I just dial in a tight bandwidth like 1/12-octave or less, cut 6-10 dB or so, and sweep the frequency knob. When you hit the ringing frequency, it sucks it right out. Only takes a few seconds. Then I push the mic level a little higher and hit the next ringing spot. Typically analog parametrics only have five bands or so, but you seldom have even than many feeding frequencies.

Not to mention, if you encounter a feedback problem during the show, especially one of those barely-ringing, just-under-the-threshold problems, you can easily deal with it with an analog parametric. Not so with the BFD.

Regards,
Wayne

[enovikoff]

Hello Wayne,

Actually, I am not looking for the BFD specifically to replace the Sabines. Most importantly, I'm looking for a way to semi-automatically use REW to equalize my "room" (church, hall, auditorium, banquet room, safari lodge, etc.) Since the BFD claims to do automatic feedback control like the Sabines, I figure after I get a BFD, I'd want to use whatever DSP hardware I have to best effect.

I'm guessing pro sound people don't like the BFD either because it doesn't do the feedback destruction as well as it claims, or because they can't make any money off of it - the $800 stereo Sabine unit I got from an "audio pro shop" clearly had a lot of profit in it for them. If I got a BFD, it would get tested in a production environment before I put it into use...

I wouldn't use REW for feedback. Betweeen roving microphones and knowing how sensitive feedback is to temperature and room occupancy, I need an automatic solution like the Sabines (and the BFD claims to) provide, in which the ringing is sensed and filtered 0.2 seconds later. There's no time to adjust a filter manually - my "customer" would lop off my head! Especially if she heard the flanging sound of the PEQ sweeping frequencies as I looked for the ringing The Sabines can do this uncannily well.. you can even stand in front of a speaker with a wireless mic And believe me, the attendees do it all the time... D'oh!

What I want to do is use REW to either program the PEQs in a BFD or manually in my Soundweb to do complete room EQ, including bass ringing as well as tonal adjustments. John's automatic algorithms aren't suitable for tonal adjustments: he'd have to implement something like the manual ones I mentioned. Even so REW is a wonderful workshop for getting the filters figured out. (If only there was a way to copy the cursor frequency into a filter field!)

Essentially, my system is a portable digital recording studio and live sound reinforcement mixing desk. It can be manually intensive to set up, but has to operate largely without operator intervention when in use.

Best,

-eric

[Wayne A. Pflughaupt]

If automatic is what you need, dbx has a model with I think 24 filters. Everything else I’ve come up with in the past Googling is lower-end stuff like the Sabine, BFD and Phonic.

Regards,
Wayne

[JohnM]

Hi Eric,

The next release of REW allows you to skip all the level setting etc and tell it to just use the mixer settings you have set up for the default device on your system, so that makes it a bit easier in apps like yours.

Full range tonal EQ is an interesting topic, and something I'd like to play around with automating in REW, just as soon as I figure out how to get a few more hours into each day Main issue for most folk is having a mic that will give an accurate measurement above the midband, if they tried full range EQ using an RS meter as the mic the result would be pretty bad, assuming the tweeters survived attempts to put back what the meter's roll-off removes. Still an item on the dev list, but a long way down...