Missing the fundamental

I’ve spent the last two months recording a set of props for the next HISSandaROAR library and the last aspect I wanted to record was via contact mics…. But which contact mics to use?

I recently bought a set of Leafcutter Johns mics and wanted to compare them, so eventually I decided the best way was to do a test recording. So here was my set up, recording to a Sound Devices 788T

1 Trance Audio Inducer contact mic L via TA Preamp
2 Trance Audio Inducer contact mic R via TA Preamp
3 BB Planar Wave contact mic via Barcus Berry Preamp
4 Leafcutter John contact mic via Barcus Berry Preamp
5 Leafcutter John contact mic via Hosa MIT129 impedance transformer
6 Dazzo contact mic via Hosa MIT129 impedance transformer
7 Leafcutter John contact mic direct line in SD788
8 Dazzo contact mic direct line in SD788

I know how the Trance Audio Inducer responds, and I know how the Barcus Berry Planar Wave responds, as I have used those mic/preamp combinations a lot. So in a way this test was to see how the other options compared. But I also decided to do a test, to verify the science of impedance matching…. hence options 5>8

To minimise phase and/or position relative to nodes, I attached all 8 contact mics and then performed sounds all over the surface of the prop… and the results? I wont upload all of the material recorded but here is a quick example:

So this file is:
1. Trance Audio Inducer contact mic via TA Preamp
2. BB Planar Wave contact mic via Barcus Berry Preamp
3. Leafcutter John contact mic via Barcus Berry Preamp
4. Leafcutter John contact mic via Hosa MIT129 impedance transformer
5. Leafcutter John contact mic direct line in SD788

To my ears the first three sound good – rich in harmonics with a present amount of bass tones. I think the BB Planar Wave sounds the best, followed by the Trance Audio – but in this example that may be placement… Leafcutter John contact mic via Barcus Berry Preamp also sounds good. If it was an instrument the fundamental is clear and present.

But both 4 and 5 are effectively missing the fundamental… If I zoom in on the low frequencies of the spectrum, it seems the Hosa MIT129 impedance transformer is not helping the situation.

Now this is not an exhaustive test by any means, when I mentioned I was doing this test on FB and twitter, a couple of people messaged me asking why am I not testing XYZ brand, and the answer: I do not own XYZ brand. I am doing this test to choose the best options from what I have today. The Dazzo mics did not seem to have the same sensitivity as the others, and by the time I had them at a comparable level the noise floor made them unuseable for my purposes. FWIW the Sanken MO-64 is the only other contact mic I am particularly interested in, but don’t have any plans for recording ants feet so I can live without it…

OK moving forwards, for these recordings I am continuing recording with these 4 channels

1 Trance Audio Inducer contact mic L via TA Preamp
2 Trance Audio Inducer contact mic R via TA Preamp
3 BB Planar Wave contact mic via Barcus Berry Preamp
4 Leafcutter John contact mic via Barcus Berry Preamp

But a final conclusion: if you plug a contact mic straight into your recorder, there is a good chance you will not be recording the fundamental frequency of the source… Whether that matters or not is up to you and what you are recording!

One thought on “Missing the fundamental

  1. Matthew

    thanks for this comparison. I had no idea using the preamp added that much. I’ll have to use it no matter what now, it’s just kind of a pain to carry it around and set it up

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