#167

Thanks for the heads-up, Rodrigo. I’ll therefor look forward to a lifetime of use. And if not, maybe they’ll let me upgrade to the DIY version by the time the battery gives up the ghost.

#168

yep ugh - just got mine with the expectation of mounting to instruments but unfortunately the gain is wayyy too high.

(anyone want it ? lol. think it was the last one for now)

#169

I was initially going to post this in the 3d printing thread, but thought it was more relevant here.

Here’s a 3d printed mount that I made for holding a (k&k hotspot) contact mic under my hihat:

Towards the end I show the sound improvement using @tremblap’s HIRT. I’m going to create a new IR today since I bought another k&k specifically so it can just live in the mount and I think the frequency response of each contact mic is slightly different.

As a point of reference here is a clearer direct/mic’d comparison between the raw contact mic, an AKG C214 and then the correction of the contact mic through an inverted impulse response:

(the recording is [raw contact mic - C214 - correct contact mic] all on the same fragment of audio)

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#170

Here’s whats happening with the deconvolution stuff.

47%20am
The green is the relative IR between the contact mic and the C214, with the black being the smoothed version of it.

The blue is the inversion of it, and the red is the gain-compensated inversion.

The output of that is then further convolved with a hipass filter to remove even more of the bass.

Here is what that looks like:
10%20pm

The red is the hipass filter, the green is the IR from the previous process, and the black is the convolution of both. All this really gets rid of is the boomy thumps when I do left foot presses, which the IR as originally inverted still leaves in.

And finally here is the difference between my previous k&k hotspot and my current one:
33%20am

Subtle, but worth recreating.
(my C214 mic position might also not be exactly right, so that could explain some of the difference as well)

2 Likes
#171

Do you have any of these recordings online?

#172

sort-of.

two short examples (nothing overwhelming) here:

then something (IIRC) buried in this release (even if it’s mostly hydrophones):

and other small bits buried in this album:

[not sure if the soundcloud links show up correctly]

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Field recording
#173

Those sound really interesting. And that is the raw recording coming out of the charge amplifier?

#174

1st two examples (on soundcloud): yes, unprocessed raw output.

“yedoma” release on Cyland: mostly hydrophone recordings, there may be a couple of sounds recorded with the accelerometer. everything there is unprocessed but the various sources are superposed + edited.

forget the last one (left.bank), it contains some sources recorded with the accelerometer but they are processed/granulated. (i shouldn’t have posted it)

#175

I recently bought a contact mic from Pickup The World pickups as I’d heard good things about that. I’ve known that they are “regular” piezo film pickups but they are shielded nicely (whereas my DIY ones hum like bastards).

I’ve not tested the pickup too much yet, but I’m curious if anyone knows what this shielding/material is that is covering the pickup is?

IMG_9750
IMG_9750.jpeg3024×4032 1.57 MB

IMG_9751
IMG_9751.jpeg3024×4032 2.17 MB

It’s textured and metallic feeling, like some kind of woven metal, but I guess flexible (and sticky?) so it encloses the piezo film.

Wondering if it’s possible to DIY myself some Pickup-The-World-style pickups from my piezo films (that have been gathering dust in a box for years!).

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#176

that looks like the kind that PTW makes for string instruments. i had one once, it was nice.

they are compressive transducers, designed to be used under substantial pressure, beneath a bridge foot. i don’t know what’s going on in the interior layers compared to the kind they make for low-pressure mounting directly on the body.

the outer material is metallized kevlar. might not be very DIYable…

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#177

I got the “Hand Drum” one, which after several emails back-and-forth with them was suggested to be a decent “neutral” one for mixed/percussive use.

The backside of it has double-sided tape, so I think this is meant for surface mounting.

Hmm, as in like (nearly?) impossible to cut and/or to shield to/with?

#178

ah ok, interesting.

yeah that stuff is hard to cut and hard to fabricate. its function as an excellent shielding material is compromised if the continuity of the weave is damaged. but i’m sure you could figure something out that does a similar job. (standard woven shielding tube, for instance.) if it’s not mounted under a violin bridge it wouldn’t have the same structural stresses.

even with the kevlar, my PTW developed severe shielding issues after some years of sustained use (bridge slippage / adjustment abraded the surface eventually.) now i use integrated pickups built into a bridge “saddle” or the body of the instrument, which feels more reliable.

#179

Little question to those of you who use contact mics in a live situation. What are your strategies to minimize feedback / Larsen problems? So far every time I’ve tried to use contact mics live it has ended in a big feedback mess…

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#180

I’ve never had feedback problems with a contact mic.

What is it that you’re using it on?
Is it mechanically coupled to the amplification in some way?
Or super boomy?
Is the feedback low/mid/high pitched?

#181

I’ve used them on several things. Mbiras, kazoos, cigar box guitar, pieces of scrap metal (like CPU coolers), tape players, etc.
The cigar box guitar I can understand. The resonant body – and the strings via sympathetic resonance – likely are a good vector for feedback, but other things I don’t know.

The feedback is always in the mid high pitched area.

I have to note that the problem is mostly that the venues have a lot of reverb (think symmetrical concrete box) and that the volumes are usually loud, like in use-those-earplugs type of loud.
My guess is that past a certain level there’s no way to avoid feedback, but maybe I’m guessing wrong.
Maybe it’s because the sounds I try to amplify are sometimes pretty subtle and hence need a bit of gain to be made audible.

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#182

Hmm, it could just be the level of amplification is creating mechanical feedback with whatever you have it on.

Does it happen with different (types of) contact mics as well?
When it does happen does it stick to one ‘node’ (per object/situation) or is it wildly feedback-y (ala an air microphone)?

If always the same mic, it might be the resonant frequency of the contact mic you’re using.

It might also be worth testing with a parametric mid EQ to see if you can dial out a specific node (again, of either the mic or room).

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#183

if that doesn’t work to identify and correct the problem, i’d investigate three options:

  • disposing the amplified objects on some foam to avoid coupling with the surface (table etc.)
  • insisting with the FOH sound person on what the acceptable highest spl is for you. (some (most…) music doesn’t need to be 105dB (or even 95dB) loud.)
  • if all else fails, sample the tiniest sounds in advance (and find a way to keep the playing of those samples gestural).
2 Likes
#184

@Rodrigo and @ermina: some great advice thanks a lot both of you!

It does yes, but I mostly have the same type (cheap piezo-based ones) and they are usually firmly attached to a body, because otherwise they wouldn’t pick up much.

Not really sure what you mean here, sorry.

I need to do some more precise testing the next time I have a proper PA at hand (next rehearsals).

Or rather, what I am thinking is to just avoid live use of contact mics (or contact mics in general) in certain venues. There’s places where you can’t say: “let’s keep the levels low”. In these cases I think your next point, or even preparing things at home, is the right thing to do, even if it takes away from the performance aspect.

I have been thinking about it as well. I did a few shows where I would just use stuff I had sampled at home. It does make the whole thing a bit more static though, so maybe I’ll try to do as you suggest and do something in-between and maybe always incorporate that in all livesets (because you never know). Possibly I can also sample things with the channel on CUE (on the Octatrack) so I can hear what I do on the phones but avoid it getting out over the PA while playing. Most of the time I do sample/loop things anyway.

#185

It would be worthwhile doing some testing with a “real” contact mic (the fairly cheap k&ks are my go-to for most general purpose stuff). Some DIY ones are made around fairly shit piezo elements that are repurposed from being buzzer/beepers, so they are design to have strong resonant frequencies in the mid/high register.

Kind of relating to my last point. If the feedback tends to get “stuck” on certain notes/frequencies, that may be indicative or it being a resonant frequency of the contact mic itself and/or the room/equipment you are using.

What I sometimes do when I am purposefully working with feedback (though not with contact mics) is I “bleed” the room during sound check, by letting it feedback and finding what the problematic frequencies are, then using a parametric EQ (in software) to dial back those frequencies. This doesn’t get rid of all feedback (and in my case, I wouldn’t want to), but it removes the problem where some frequencies just dominate everything and/or lead to feedback when you don’t want it to.

2 Likes
#186

Good idea!
I do have mostly shitty piezos I have to admit. At least I guess they are, most of them I haven’t made myself. I only have one good one from Jez Riley French, but I haven’t used that one live yet.

That’s a great thing to do indeed! Thanks a lot!