Anyone used Impulse Response Utility for IR yet?

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Level 1

9 points

Anyone used Impulse Response Utility for IR yet?

I just read the Impulse Response Utlity PDF last night.

I'm gonna try and capture some rooms & some hardware stuff etc.
Seems like its down to getting/picking a decent (flat) playback system (mobile)... as well as Mic choise of course.

But lo-fi might have cool results too.
Any tips.. stories?
What to use for power for the pre-amp, mic, rig etc in the field?

MacPro Octo 3.0, Mac OS X (10.4.11), MacPro 8 -3.0 I SX3 I Logic 8 I Metric Halo I/O I MTP-AV I UAD-1 I TC Powercore

Posted on Dec 31, 2007 8:50 AM

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Answer 1

Jan 1, 2008 8:25 AM in response to deepswing

Lo-fi definitely has its place. Lots of cool things to try, limited only by your imagination. Try taking a Shure SM57 and swing it in a circle in front of a guitar amp while the sweep is going. High quality is challenging and fun. You need a good condenser mic, I recommend using it in omni for the most natural sound. You can make a stereo impulse with just one mic by moving the mic or the speaker. Do the left one, move the mic, and do the right one etc. The speaker has a big impact on the sound, so the better the speaker and mic, the better the impulse. Make sure there isn't too much noise in the room, if there is noise, you'll need to be loud with the sweep. Also keep in mind that you can use the IR 100% wet, so place the speaker where you might place a performer in relationship to the mic. Low frequencies can get boomy and weird, so using a smaller speaker can help there. I have been experimenting with moving the mic or the speaker during the sweep, so the there is a spectral spread across the room. Not accurate, but very cool. I've done thousands of sweeps. Also, sweeping outboard effects processors like reverbs work well. I play the sweep thru my Lexicon reverb and into the room and capture a long Lex reverb in my small tracking room. I've gotten lots of very use-able reverbs with that method. Experimentation is the bottom line. The IRU is easy to use, and it makes it fun to do. If you want to go outside and capture stuff, forget the sweeps. It's too much of a pain to find a way to power the speaker in a forest. Just record some loud explosions, like an M-80, and use that as the impulse response, don't use the IRU. I've tried clapping two 2x4's together, but there isnt enough low end to get a good impulse from it. Same with a starter pistol. No low freq's.

My main rig consists of a Dynaudio BM15 powered speaker, a Metric Halo ULN-2 mic pre/interface, a 2.4 GHz Macbook Pro, and 2 Neumann KM183's which are omni diffuse-field mics. I also use an AKG 414 TLII for guitar cabs and stuff that require close miking, in cardioid or omni or whatever.

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Answer 2

Jan 1, 2008 8:32 AM in response to John Buehler

Also, when sweeping outboard effects, do not use anything that has a chorus or flange. Things that affect pitch over time do not collapse into an impulse, it screws it up. And there are lots of reverbs that have a chorus tucked away in there, turn it off.

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Answer 3

deepswing Author

Level 1

9 points

Jan 1, 2008 9:59 AM in response to deepswing

Hey.. thanks for the info. I did some testing in my studio yesterday.
I got some nice results, but lots of questions. Many due to not knowing exactly how this thing works.

1. When cabling thru some hardware, should we always get the hottest gain possible in IRU metering? Right B4 clipping?

2. Same with sweeping in a room? Should I set my playback system to the loudest possible? How about my Mic Preamps for recording that room? Hot as possible? Will a IR sound diff/better at diff capture levels?

3. With a loud sine sweep... my room has some sympathetic frequencies (rumbles in the walls etc) Will this affect my IR? I couldn't hear it in the IR applied yet.

4. So OMNI is a good setting. Is this for mono & stereo recordings? I am more a songwriter, so I don't have that much experience with phase issues etc.

5. If I record a ST IR .. one mic at a time, is placement of the 2nd mic crucial?.. or can I just place it in the other side of the room?

6. When trimming the intro of the waveform, is it crucial to clip right up againist the transient? If there is a small space left, would this act as pre-delay or something? Again, not sure how this works.

7. Same with the ending? Should it always be shortened? I did some of my 6176 & Neve Preamps. Does Space Designer just play that short transient over & over applied the your signal?

8. what about noise before the main transient? Should you always apply a small fade in? Does this matter?

9. When auditioning, the Wet/Dry doesn't seem to work.

10. How do I make a recorded spike, as mentioned in L7 manual. (i'm in 8 now)

11. Why isn't there a gunshot inclued in IRU like the sweep?

12. The manual says that SD can use recordings of gunshot recording as there are w/o the IRU. How does it do this? Doesn't it have to have the gunshot recording to remove from the IR? Understanding this will help me do this type of IR.

13. Can we use a "recording" of a M-80/gunshot? If no, then why? Are there full freq "recording" out there we could use?

14.I did my FenderTwin with a C414. I think it has a bad hum problem. Will issues like this affect the IR? I haven't had time to actually test these yet.

15. I'm looking forward to capturing the stairwell in my studio building. I read that some classic recordings used the stairwells in NYC studio buildings. How far away should I place my mics? 5 feet..... 5 floors? 🙂

16. Is there a USB mic out there with a decent flat response, or is this route not even worth it?

17. Do you find the 10 sec sweep better than the 50 sec sweep?

18. Can we use any signal for experimenting. ex: loud claps?

I am about to capture... my cassette deck, Rhodes Suitcase cab, .. and even drop a small mic into an empty water jug bottle.

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Answer 4

Jan 1, 2008 3:55 PM in response to deepswing

Man. Ok.

1) The use of a sweep allows for a more forgiving level environment, and being 1 db away from clipping is not necessary.

2 and 3) Making things rattle and rumble would be a good reason to turn it down. It's the relationship to the ambient noise level that defines how loud it should be, in my expereince, it shouldn't be so loud that is uncomfortable to listen to standing there.

4) Omni is the most natural sound, cardioid has off-axis coloration. Experiment after you've played with omni for a while.

5) If you are going to just move them around, a general rule of thumb is no less than 6 feet away from the previous position to avoid phase problems.

6) Yes, it would be like a pre-delay, and you can trim it or adjust the start time in the SD preset as well.

7) An impulse is more than just a transient, it is a snapshot of the frequency spectrum collapsed into a single moment. Different boxes can have noise or grit at the tail, which is why you might want to trim it. But it's best done in space designer after the impulse is made, at least until you get a feel for it.

8) Noise is noise. If you want it, good. If you don't, trim it.

9) Works fine here.

10) A spike can be made without using the IRU. The IRU makes a spike out of a sweep. Instead, just record a loud short hit and use that as the impulse. No need to convert it into anything. Much harder to get a clean reverb, the signal-to-noise ratio is tough.

11) Because it's all about using the gun in the room you want to capture. I've tried pink noise bursts out of speakers. Sweeps are better.

12) The fundamental difference is that a gunshot does not need to be made into an impulse, it is one already. Record a firecracker in a room. Trim the recording and use it in space designer. Or hit a snare drum. You'll see.

13) Sweeps are better. Yes you could, I've tried, and sweeps are better.

14) You will hear the hum.

15) Do many positions. They are all valid and different. I like the far ones mixed with some dry original.

16) Not worth it. For anything beyond quirky lo-fi at least.

17) 10 secs is better because it's less likely to have some noise occur during the sweep. 50 has a better signal to noise. I usually use the 10.

18) Claps have no low end, so the result will be thin and lame. Sweeps are better. I have used a couple of wicked lightning cracks that work nice for the odd guitar solo or whatever.

The IRU is only for sweeps. It is the best method IMO. If you just make a loud short sound, the impulse is done already. Take it straight to Space Designer.

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Answer 5

deepswing Author

Level 1

9 points

Jan 5, 2008 9:10 AM in response to John Buehler

Hey John,
Thanks so much taking the time to reply to all that!
I've done some more work with this stuff now.
I've done my apt building parking garage, studio stairwell etc. I even dropped a small Sony mic into an Arrowhead water bottle. It sounds like junk when tested on a voice etc, but I tried it on a snare drum, and it had very cool uummmpphh.
Did my Neve 1272, boomboxes etc. I evn dropped small mic inside my Martin guitar body.
Some of my IRs seem to had a lot of mud swirling around in the low end area. Some I can even seem to hear part of the sine sweep contained in it. Not sure how to fix that.
I did some kids audio toys also. they have a very cool sound when used in Logic! I'm going crazy doing this stuff now. Now I'm writing a list of all the Locations I want to capture, like the Hollywood Bowl... bathrooms... inside my piano... just for my own library.

Of course I have a few more questions now.

1. When I record a sweep for some items, my level is very low, but when I collapse it down it seems to show a red area that peaked (distorted). Even if I lower my signal very low, it still seems to do this. It is a problem for the final result? I expect it is distorted, but will it make my IRs no good?

2. Will a mono IR work on a Stereo insert for Space Designer? I did my cassette deck, but it was in mono, and I could not hear anything when I tried it out, but it was a mono test.

3. I had good results sweeping & using a stereo setting, and recording one mic at a time, then moving it to the other side of the room. Then I also did this trying a clap with the sweep set to off. These had cool results also, but how to I get the two stereo claps in time? They are alway off a bit, and it makes a type of slap back effect for the IR, which is ok for some things.
Even though a clap in a room does not capture all the lows & highs, it is a type of lofi IR to have. I did a great one in my main room of my studio, and it is great when applied to my martin. I just opens it up (used with one of the moved mic stereo IR).

4. From number 10 on my questions list, I read that you can make a short digital spike in Logic using the pencil, and use that to playback and capture. That is what I was referring to for that question. Just wanted to know more about that.

5. I would still like to understand how SD uses a file of an impulse in a room, and does not use the clap/gun sound .. and only the ambience of that recording. I thought it had to remove the original sound from the recording and what was left, was the room sound, and that would be applied to your mix. I thing it removes the sweep, so how does it do it for the other type?

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Answer 6

Jan 8, 2008 3:09 PM in response to deepswing

I've been setting off big loud fireworks out on a frozen lake in Wisconsin for the last 2 days. The IR's came out great. I'm still amazed that we can do this at all. Now for your questions...

1) I have not seen this myself. Not sure what the problem is, but if the IR is clipped, it's not good.

2) Yes, I believe the mono impulse will work on a stereo SD instance, just gives you mono out of 2 channels.

3) The problem with claps is that they are always different, so you always get a different sound with each clap. Lining up 2 claps can't be done in the IRU. You would have to line them up in Logic, edit it there, and then combine them into one stereo file, and use that as the impulse in SD.

4) That method is for Digital connections from the computer to the outboard box and then back to the computer. It can't be used over analog cables. I've tried that method a lot and I can't get enough of a signal to noise ratio out of the impulse. I prefer the sweep method. If you want to try it, you have to go digital both in and out.

5) The IRU makes spikes out of sweeps. The resulting spike is a collapsed version of all the frequencies at once, with their reverb tails lasting beyond the original tone. That is the same thing as a short loud sound like a clap or a gun or whatever. The only time there is any "comparing" done is when the spike is made into a sweep. Once the IR is made, it has all the info SD needs to generate a reverb based on the IR. A gun does not need to go through this process because it already is a snapshot of all frequencies firing at once. It's kind of like radar or sonar. The "ping" is always an approximation of a true impulse, which is theoretical, and not physically possible. Given that we know the start time of the impulse, SD can assume that all that follows is the reverb. Does that make sense?

Message was edited by: John Buehler

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Answer 7

mattrixx

Level 3

945 points

Jan 13, 2008 2:15 AM in response to John Buehler

Guys, I have really enjoyed reading about what you have been experimenting with. Fantastic.
Wow, I would love to hear the results of the Fireworks on the Lake!!

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Answer 8

deepswing Author

Level 1

9 points

Jan 13, 2008 9:50 AM in response to John Buehler

John Buehler wrote:
I've been setting off big loud fireworks out on a frozen lake in Wisconsin for the last 2 days. The IR's came out great. I'm still amazed that we can do this at all. Now for your questions...

Thanks for your "responses"... haha
Very helpful to me.

I remember long ago reading about Rush recording some things across the lake for natural FX.
I would love to hear your lake IR also!
I have dropped a small mic in a large Tuperware bin, and placed my speakers outside it. It sounds great on a drum kit, for cool FX.
Some of Stereo claps I've done are not lined up, but create a cool stereo image, even though they are not the same, as you state. Not perfect in that sense, but sometimes that can be good (since many projects are electronica stuff). Anything goes.

I have now done more in the old bank lobby where my studio is, and lots of others.
I will post many of mine over at LogicProHelp.com when I have cleaned them up.
John, are you making these for your private collection, or would you ever post any? Are you a sound designer or producer... or both?
Would love to hear some.

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Answer 9

Jan 14, 2008 10:11 AM in response to deepswing

I'm actually doing the IR's as a work for hire, so I can't share them until the project is completed. Anything that wasn't used I'll be able to post. But it will be a while. They are also pretty much all done in surround only. I use a Decca tree setup for the front using AKG 414 TLII's, and Neumann KM-183's on a Jecklin disk for the rear. I am also deeply involved in nature recording, and use the same setup for that as well. I have a website coming that should launch sometime near the end of February or early March where my stuff will be available. My thunderstorm is the best. The challenges of recording outside have made the difficulties of recording indoors seem non-existent. An out of tune guitar or a ground loop is nothing compared to being charged by a bear or having my entire recording rig get trashed by a storm that got really bad really fast. And I totally love it.

I am a composer and engineer. I've done the score and mix for the Sky Shows at the Adler planetarium here in Chicago, lots of TV and radio spots for the White Sox, but primarily I do the score and post for documentaries. I was chief engineer at a Chicago studio for 15 years until I started doing more composition, and now I work from my home studio.

The IRU is a wonderful tool, and I encourage anyone reading this stuff to try it out. It's just too easy and fun. There is no limit to what can be done IMO. There's nothing like having your own reverbs.

Also, I do everything at 24-bit 88.2. There is a real difference between 88.2 and 44.1.

I check this forum daily, and will try and help anyone who has questions.

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Answer 10

deepswing Author

Level 1

9 points

Jan 15, 2008 11:08 PM in response to John Buehler

http://www.logicprohelp.com/viewtopic.php?t=19844

I did a quick tutorial (test 1)

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