Is this a standing wave problem?

[ShadowAMD]

Originally Posted by garth8

I could use some help in identifying this problem please.

I need to figure out if this sound in my recordings is a standing wave issue, digital noise, or something else. I've attached an mp3 sample to listen to. Can you please listen to it and tell me whether you think that's a standing wave issue or not? I'd like to know if I'm barking up the right tree.

I have a small recording room about 12 feet long, by 10 feet wide, by 8 feet high. It is treated but I'm thinking its just too small to deal with the standing waves. I've got the corners of my room treated along with most of the ceiling. I've also put traps under the microphones but I still get this noise.

This background buzzing/noise is on most of my recordings though I notice it on some songs more than others, maybe cause the standing waves are excited by certain frequencies?

I haven't edited the audio sample at all so its raw. Volume may be high so put your volume down first as a precaution.

I have a smaller room than you and I don't suffer, sure your not recording it too hot? Should be -18dB dry.. It's a shot in the dark but hey it could be right

[theblue1]

I'm not entirely sure what sound you mean. At first I though I didn't hear much except a tiny bit of room and circuit ambiance and guitar and human noise.

But then I thought about what you were saying and thought, maybe I'm looking for too small a detail...

By 'buzzing' do you mean the somewhat rhythmic beating in the guitar, particularly in the bass strings? I'd assumed that was a characteristic of your guitar, but I tried imagining it a different way and wondered if it might be a resonance characteristic of the mic you were using.


For reference, most people's problems with standing waves tend to manifest at the bottom end as a boomy resonance in the room -- say when you hit certain notes, the room seems to boom somewhat.

You can use calculators like this standing wave calculator, to calculate the resonances, but it can be a bit daunting to really make sense of it all.

[garth8]

Hmmmm yeah this sound is really subtle so it may be really hard to discern. I'm listening back with AKG 701k's and those tend to reveal every detail/flaw.

Listening back to some older recordings. Right now I'm using spaced omnis which would pick up more room sound. Before I was using spaced cardioids which would pick up less room sound. So until I get a bigger room to record in I should probably stick to cardioids.

I just did a test with very low gain levels, well under unity levels, so low they barely register. I still hear it. It happens in both the vocal and guitar preamp with completely different mics.

It's like a resonance that is most pronounced when I first strike the chords, its seems to be mainly one main frequency with some other standing room modes chiming in here and there at lower volumes. I'm going to see if i can somehow pinpoint it. It's rather difficult though since I can't just isolate it without exciting it with sound waves so its a sort of catch 22. Its hard to pinpoint under the sound of the guitar.

[garth8]

I played single notes all the way up the guitar. You can hear it mainly on the A string. I've uploaded the A string wave file at highest quality 96k and 24bit. MP3 seems to mask it a little so I managed to get a wave uploaded of the most critical part.

You can hear the problem mostly on note 2 and 11. Starting with an open string and ending on the 12th fret so 13 notes total. The sample is attached.

[mcgruff]

You will certainly have standing waves in such a small room. Try this test.

However, I think it's more likely that the guitar has a wolf tone. That should be pretty obvious if you take the guitar outside and it sounds the same.

You can play around wolf tones to some extent by picking the string near the bridge but of course you're losing some expressiveness if you're forced always to play certain notes that way.

You can also do a lot to tame wolf tones with a multi-band compressor. Tune it in carefully to the problem frequency band and apply limiting/compression as necessary. That can sometimes work quite well but if you listen closely what's left after knocking off the peaks may not be as pure and clean as the tone from other strings.

I've also had some success with blobs of blue tack. Feel around the top while you play to find which bit vibrates hardest on the wolf tone. Obviously the whole top vibrates while you're playing, but you'll probably find one bit (probably near the bridge) which vibrates particularly hard at the problem frequency. Splat a blob of blue tack on there and experiment with different sizes of blobs. You don't want to add any more mass than you have to. If you've got a luthier whom you work with they could probably figure out a more elegant and permanent solution.

[garth8]

Thanks for listening and helping everyone.

Thanks for the link to the tests, I'm going to try those out. I was thinking maybe there was a site out there that had examples of what standing waves sound like with examples like the one I made. Most of the sites I found are just written explanations that I've read before though. Nothing like samples to confirm theories though. I'm pretty sure this is a standing wave issue, I was just looking for confirmation.

I don't think these are wolf tones causing the issue because I get this on both of my guitars, one classical, the other steel string. Unless both guitars are problematic or this is a combo of guitar and room problems.

There was a mention of Mic resonance. Do standing waves or other hard frequencies trigger it? I wasn't aware of that issue. That could be a possibility.

[garth8]

Problem solved: I was reading another thread on possible drivers in the headphones going bust and they mentioned checking for hairs against the driver. I cleaned up the drivers with a q tip. Problem solved. Wow, can't believe it was just that. lol

Anyway now I know. Maybe someone else can benefit from this too. Bye thanks.