Topic: what does brickwalling sound like?

[skokiebob]

Hello all, got a question, When you have exceeded your mic's max SPL, does it sound the same as clipping? I had a couple really loud shows where my levels seemed okay, no clipping indicated, but when played back they had loud pops even worse than the distorted sound of clipping. So I'm thinking thinking they got overloaded?
soundpro cmc8's>spsb preamp>R09,  as always thanks for your help.

[Arni99]

I guess your levels were ok on the peakmeter BUT you overloaded your line-in with too much gain from the preamp. I never use any preamp gain for loud rockshows - in this case my preamp is a usual battery box supplying the mics with 9V set to 0db preamp gain.

What was the gain-setting on your preamp?

remember=> you could set your preamp to +30dB and set the level on your recording device peaking at -12dB and then your line-in gets extremely overloaded by your preamp signal.

[skokiebob]

Thanks Arni, Chris from Church was telling me the same thing that the signal from the preamp doesn't get measured by the digital R09 totally, or something to that efect, don't want to misquote Chris. I'm sure I should do as you say and at loud shows leave the pre at 0 and just let it power the mics. Hope I get the hang of this soon, lot more fun to get good shows to listen to and share!

[Church-Audio]

Thanks Arni, Chris from Church was telling me the same thing that the signal from the preamp doesn't get measured by the digital R09 totally, or something to that efect, don't want to misquote Chris. I'm sure I should do as you say and at loud shows leave the pre at 0 and just let it power the mics. Hope I get the hang of this soon, lot more fun to get good shows to listen to and share!

When your levels are good on your recorder. But you have distortion that indicates that the distortion is most likely because your preamps gain was set to high for your line input, or your preamps input or microphones overloaded. The problem is pretty complex but to simplify things, what can happen is you have a really hot output from your preamp and then you attenuate via your recorder. The problem is your recorders attenuation is not analog its digital so there is no "hard" attenuation going on. This is where the problem lies, if you attenuate digitally you still have the possibility of overloading the first stage of your recorder with out even knowing it because your level meters look ok.
I always suggest getting to know your gear in your house with a stereo and a pair of headphones find out how loud you can crank that stereo before things go wrong. Then you will have a better idea of how much gain your preamp can give and how much input your recorder can handle.

[Mike R.]

I know this doesn't help much when you're doing the recording, but it's pretty easy to recognize what brickwalling LOOKS like.  In your audio editor (I use Audacity) look at the waveform display.  Even well zoomed out, if it looks like all of the peaks are exactly the same height, and that height is lower than full scale, you've probably got some kind of clipping going on.  Most audio just isn't that uniform.

When you zoom in on a peak, if you see that it's not sharp or rounded, but flat, there's your clipping.

Harder to describe what it sounds like, but to me it just sounds very harsh.  Basically, you've got a lot of high frequency energy (that doesn't belong there) in that sharp corner when the waveform flattens out.

I'm pretty certain that my PMD-660 (oade mod, but applies to stock also) has a fixed gain on the mic preamp, so if I'm in this situation, the only remedy is to reduce the input level by switching in the pad (either in the mic or the 20dB pad in the box) or locating the mic somewhere quieter.  I think the signal chain looks like the following.

mic >> (switchable pad 20dB) >> preamp >> gain control >> meters >> analog-digital converter

so if I'm clipping in the preamp, my only remedy is something to the left of that in the chain.  If I'm clipping at the ADC, I have more options as to where I can fix it.

Hope this is helpful (or, for that matter, correct!)

[Roving Sign]

You can see it in your meters - They wont bounce quite like they should...they will tend to not go below a certain mark. Its not super-obvious...(well, depending on how bad the brickwalling is)

But - your meters can give a hint...

Brickwalling will sound different depending on the music and mics - for example - omnis at a bassy show will make a farting sound - and mask the higher frequencies.

[skokiebob]

Can't thank you who (yoohoo?) responded enough! So this begs the question, are there digital preamps that will get measured accurately by a digital recorder? Is this a function of an A/D converter? Or am I missing another aspect of this sometimes "way-over-my-head" process. 'Cause from articles I've read, the digital and analog worlds are miles apart.

[pmonk66]

I used a CA-9100 with the +20 gain going into a stock pmd660 while using AT-831 with the levels set between -6 and -2 at loud rock shows (Gov't Mule and Roger Waters to name a few) and the recordings came out great.

I recorded Rose Hill Drive at CBGB before I got the CA-9100 and talk about brickwalling