Topic: loud concerts and a cheap mic

[Microbe]

Petur,

I'm using the Church cardiod mics and ST-9000 pre-amp.  I have my recording levels set as -2db to +2db on the Iriver and 0db on the preamp with the output level set at full.  I've recorded a rock concert at 5 ft. from the PA.  No distortion.  I also do not use AGC on the Iriver, my levels are slightly lower than yours, when I compare raw Wave forms.  Are you sure it's not the AGC causing your problems? While recording are you trying to get your levels as high as possible and letting AGC catch the mistakes?  I tested the AGC and just didn't like it because the actual internal settings weren't explained clearly.  Just food for thought

[Church-Audio]

Are you using AGC? If so turn it off, 99% of the time the problem with the distortion is Automatic gain control. That system is an old carry over from Sony's MD days, and is designed for recording speeches not music. Speech has a much more predictable pattern and thus it can be anticipated by AGC systems. Music has too much of a dynamic range for any Automatic gain control chip to ever be able to calculate. It also eliminates an unnecessary source of noise in your recordings because automatic gain control will always ramp up quiet passages and ruin the dynamics of any recording and decrease your signal to noise ratio.

Well the first gig I just recorded was a bit of a disappointment

The gig was pretty loud and I had the preamp switch set to -27dB,
AGC (safety mode) turned the gain down to -4db (YUCK!).
(This is on an iriver h340 with rockbox btw....)

Guess what: the drums and bass parts are distorted! Looking at the waveform I see no clipping but either the output of the preamp was too high or the mics/preamp can't handle the soundpressure.

So I don't know what to do... I was expecting *a lot* from this kit

to end with a positive note, the recording otherwise sounds quite good

edit: I've put a small part of it online (zipped wav) for your hearing (dis)pleasure: http://users.pandora.be/mieke-en-peter/distortion.zip

[petur]

Yes, I have AGC enabled as software algoritm in my rockbox build, I use it in a safety mode, that is: the only thing it does is turn the gain down if there's clipping risk. I had started it on 0dB and it had changed it to -4dB by the end of the show. It does not turn up gain again.

I haven't checked the AGC code but I think it decreases gain if the signal goes above -3dB for additional safety.

I had my gear attached to the fence in front of the stage (about 2 meters from the stage). I think spl was even worse further back because the PA was left/right of the stage and only pointing to the back. Maybe I should have a talk with the sound engineer about turning the volume down as I know the band pretty well...

The mics/preamp I got was:

• STEREO MICROPHONE PREAMP ST-20A
• B-99M PROFESSIONAL BINURAL MICROPHONES

Chris, you can PM me regarding trading the pre-amp. Does the other pre-amp have bass rolloff? Because the mics pic up such a wide range I now consider it usefull (it was never an issue with my old cheap mics because they didn't go that low)

A last remark: as the level was pretty high on the iriver input, I wonder if the iriver input wasn't overloaded. I'll try to check that some way.

edit: tried to overload the iriver input but it was hard to find a source with levels high enough. I only saw clipping, not what I saw on my recording....

[Microbe]

It could very well be the SPLs overcoming the mics then.  I'm not sure what the your country's standards are on concert db levels.   But it's hard to say exactly what the noise is, the sound could also be stuff shaking around on stage. I know when I'm that close I pick up the bass rattling around the drum heads.   I don't have Chris' Omini's so It's hard for me to comment, maybe I'll pick up a pair to experiment necause I don't have that problem with his cards.

[petur]

Well I'm pretty sure neither me or my wife heard the distortion (during the performance) that's in the recording.
I remember my ears hurting a little from the guitar part but listening to the recording completely, I am convinced the bass and bassdrum are overdriving something.

I'm going for another pre-amp, I just hope it won't turn out that the mics get overloaded

[Microbe]

Petur,

Good luck!  I'm hoping it's not the mics, but just remember your omnis will pick up more bass than my cardiods will.  Which may help aleviate your problem.  Chris will know best though.  I'm crossing my fingers for you.

[petur]

one more question:

As I'm going for the st-9100 of Chris, I'm wondering about its high-pass filter:

12db per octave @80Hz

Will this not take away too much of the bass?
What's the advantage <---> not use it and postprocessing?

And does anybody (Chris?) know what the max spl is the B-99M PROFESSIONAL BINURAL MICROPHONES can handle.

[Microbe]

Here's a link to a thread where people discuss some of the issues of Bass rolloff vs post production. 

http://taperssection.com/index.php?topic=66326.0


I don't have any experience with the ST-9100 so I can't comment on it's rolloff

[Church-Audio]

Hi you do not need to use the high pass filter but its there. I have designed it so that it will not effect freq's above 110hz so you do not lose the warmth of your recordings. I think its always best to try settings on the opening band first and see how things go. I think that its better to have a clean recording with less bass that can be easly bumped up in post. The thing to remember about bass roll off is this using it reduces bass of course but the bass is still being recorded its just bumped down. What I am saying is the bass is still on tape its just -12db down its easy to "undo" a bass roll off at 12db per octave just and a bass boost and put it all back. I have done it many times. what happens is with the high pass filter on you can get hotter levels to tape ( just an expression) we all know no one uses tape any more. The hotter your levels are to tape the nicer your recording will sound but if there is to much bass in your recording this eats up your headroom and causes you to set levels too low this makes for a bad recording IMO. Good luck and let me know if there is anything I can help you with
Remember the bass roll off can be switched on or off it does not have to be used.

Chris Church

one more question:

As I'm going for the st-9100 of Chris, I'm wondering about its high-pass filter:

12db per octave @80Hz

Will this not take away too much of the bass?
What's the advantage <---> not use it and postprocessing?

And does anybody (Chris?) know what the max spl is the B-99M PROFESSIONAL BINURAL MICROPHONES can handle.

[petur]

having some gigs coming up but not the new mic amp, I decided to do some experimenting.

I've connected the mics of Chris directly to the iriver h340. Of course this means they'll only get 3.7V power.

The amazing thing is that the distortion sounds exactly the same as with the mic amp. The iriver was set fixed at 0dB gain. A small WAV file is here: http://users.telenet.be/petur/distorted2.wav

On my way to the gig I rememberd I still have a skytronic battery box around which I modified to take 9V, so I'll try that  sunday.

BUT... I get the feeling the distortion is coming from overloaded mics

[Microbe]

Hi Petur,

You're still picking up a lot of bass.  When you get the new preamp with bass rolloff you should notice a difference.  I have a sample posted in the gear loan section under church cardioids.  The cardiods cut out some of the bass by their very nature (not as much reflection coming back).  This sample was recorded on a H120 with st-9000 pre-amp 3ft from the stage and PA stack.  Check the last page in the thread:

http://taperssection.com/index.php?topic=61141.new#new

[petur]

You're still picking up a lot of bass.  When you get the new preamp with bass rolloff you should notice a difference.  I have a sample posted in the gear loan section under church cardioids.  The cardiods cut out some of the bass by their very nature (not as much reflection coming back).  This sample was recorded on a H120 with st-9000 pre-amp 3ft from the stage and PA stack.  Check the last page in the thread:

http://taperssection.com/index.php?topic=61141.new#new

Yes the concerts I'm taping are very bass heavy, much more than the sample you posted (which I find lacks a bit of bass). I could do with picking up less bass, but my fear right now is that if the mics get overloaded by the bass, the roll-off filter won't help that much. The st-9100 will certainly help a bit to lower the bass and make the signal less hot on my iriver. But it won't help if the mics are distorting

So I'm very much thinking if I should get other mics too. And I'd better decide on that *before* Chrish ships the pre-amp. The sad part is I'm missing some good recordings. The one last night was one of the best the band did. At least I was there to enjoy it

[Microbe]

Petur,

I record pretty close to the stage and PA, but I tend to go more towards the guitar side of the stage.  This is to help me avoid the high bass SPL level.  Is it possible you can move your position to a better balanced spot?  I've been looking at mics from microphone madness because they have a higher SPL rating.  They have a lower bass frequency response though.  So there's always a tradeoff somewhere.

[petur]

been there, tried that.... there's just too much bass

[petur]

AAAAAARRRGGGGHHHH

right, that was concert number 4 completely ruined by distortion, it wasn't even very loud.

This time I tried the B-99M PROFESSIONAL BINURAL MICROPHONES of Chris with a 9V battery box directly into the iriver. Gain set at 10 and still had a reasonable margin.

I don't know what to try next, but I have a *very* strong feeling th st-9100 pre-amp won' t solve (all) my problems.

So I'm now open to suggestions for other mics.
Remember I want to tape bass heavy rock concerts, the mics should be able to handle quite a few spl.

I'm now at almost 3x my planned budget and *very* dissapointed. My next gigs will be taped with a $20 mic that sound awfull but at least doesn't distort       

sample: http://users.telenet.be/petur/distorted3.wav

more thoughts: have I made a mistake somewhere along the thinking process? Can it be that the mics don't work well with the cheap skytronic power box (normally operates on 1.5V but modified by me to take a 9V battery).