The New Metal Marshmallow Is Here

Buy a Marshmallow

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Marshmallow is a piezo disc contact microphone with a nice high-impedance preamplifier. It is used to pick up sound waves traveling through solid objects, without also picking up sounds travelling through the air.
  • 'Electrify' acoustic instruments: Just stick Marshmallow to a guitar, cajon, or whatever, and it will pick up only the sound of the instrument while blocking out external sound traveling through the air.
  • Make unusual recordings: You can stick Marshmallow to walls, tables, metal sheets, ceramic teacups, eggplants, etc..., and record scraping, scratching, tearing, plucking and other strange sounds.
  • Use as a sensor for scientific and research applications: You can stick Marshmallow to the ground to detect footfalls, you can use it to tell how an object was struck, or, using three, you can triangulate the position of tapping on a wall. (These examples would require additional software which is not included).
Archival information about the discontinued Original and Burnt models is here, along with a product comparison


  • Built-in mic preamp: Other high-end contact mics require you to buy a separate preamp, often for an exorbitant price. Marshmallow has a builtin preamp that was specifically designed for this purpose. It boosts the signal and solves impedance-matching issues associated with homemade contact mics.
  • Excellent bass response: Other contact mics in the same price range are just piezo discs solderred onto guitar cables. As a consequence, they have very poor bass-response, giving them a tinny sound. Marshmallow's built-in preamp that solves this, giving it a full, rich sound.
  • Flat frequency response: Flat across the entire audible range. A Bode plot of this is shown below.
  • Plug it in to anything: Unlike traditional mics, Marshmallow has internal circuitry that makes it compatible with any audio equipment. You can plug it into a high end mixer or audio device, or (using the appropriate adapter) you can plug it directly into the audio input on your laptop. You can even plug headphones right into Marshmallow and use it like a stethoscope (although note that contact mics are not great at recording heartbeats because not much energy is transferred from the human body into the microphone).
  • Impervious to hum: Contact mics and amplifiers act as small antennas that pick up tons of electromagnetic radiation which can be heard as loud humming, buzzing, and clicking in the audio signal. Metal Marshmallow was carefully constructed with a shielded aluminum housing housing, so the signal is hum-free at all times. Metal Marshmallow is the quietest contact mic on the market.
  • Small physical size: Metal Marshmallow is 39 mm in diameter and 30 mm tall. The entire length, including the audio calble and connector is about 21 cm. It weighs 80 grams.
  • Long battery life: Metal Marshmallow will last for at least 10 days of continuous use. After that, it can be recharged via the USB connector. It takes about 1 hour to charge.

Frequency Response

Bode Plot Details about how I measured this are on my blog, https://ambisynth.blogspot.com/2019/04/how-i-calibrated-my-contact-microphone.html.


Images of Marshmallow with different parts labelled
Images of Marshmallow with different parts labelled
  1. Sensor: The actual audio sensor (piezo disc) is inside of the metal housing, on the flat side that is closest to where the audio cable enters the housing. This side should normally be mounted to whatever you are trying to record.
  2. USB Charging Receptacle: Metal Marshmallow has a builtin preamp, which is powered by a builtin rechargable battery. USB is used to charge the internal battery. The recptacle accepts a standard micro-USB charge cable, such as is used to charge many cell-phones. The charge time is one-hour, and the battery will last at leat 10 days, whether or not you are using the microphone. Note that Marshmallow does not use USB for audio, only for charging.
  3. Charge Status Light: This light will come on while Marhsmallow is charging, and will turn off once the battery is full.
  4. Audio Cable: This is standard shielded instrument cable.
  5. Audio Connector: This is a standard 1/4 inch mono (TS) female receptacle, which accepts a standard instrument cable. Marshmallow can then be plugged into any regular audio interface or mixer.


Images of Marshmallow showing how to install batteries
Metal Marshmallow has a built-in rechargeable battery that powers its awesome preamp. It will ship with the battery drained. Prior to use you must charge it via a standard micro-usb charging cable. The charge-status light will come on when it starts to charge, and turn off when it is done charging. It takes about 1 hour to charge, and will last for at least 10 days of continuous operation. To reduce noise, Metal Marshmallow does not have a power switch; It is on all of the time until the battery drains. While it is technically possible to use the microphone while it is charging, this is not recommended because the internal charging circuit is a strong source of electromagnetic noise that will cause a loud humming or buzzing sound in the audio signal.

Tech Specs

  Metal Marshmallow
Gain 14dB (white), 24dB (red), 34dB (black)
Housing Color Silver
Housing Material Milled Aluminum
Housing Diameter 39mm
Housing Height 32mm
Battery Type Rechargeable
Battery Life 10 days
Recharge Time ~1 Hour
Charge Indicator White LED (on while charging, off when done)
Hum Protection Built-In
USB Connector For Charging Only
Audio Connector 1/4" Female Unbalanced TS


Marshmallow is available in a few different gain variaions. The standard model has red heat-shrink on the audio connector. This mic is good for most things and corresponds to the discontinued burnt marshmallow. There is additionally a low-gain variant with white heat-shrink that is better for recording loud sounds, like percussion, and this corresponds to the discontinued original marshmallow. Finally, there is a black heat-shrink model with high gain, that is good for recording very, very quiet sounds. If you watch closely, in the video above, you can see which variant I have used to record different things, which should give you a general idea of how they behave, although in many cases any of the mics would work just fine for a moderate sound source.

  Color Gain Decibles
  WHITE 4.7x +14 dB
  RED 15x +24 dB
  BLACK 47x +34 dB

Plug It In

Images of Marshmallow showing how to plug it in to an audio device

Origin Story

Hi, I'm Michael Krzyzaniak, creator of Marshmallow. While I was getting my PhD, I was building robots that played music. I needed the robots to listen to themselves while blocking out other sounds, so I thought I'd use a contact mic. Unfortunatly, due to questionable engineering, electromagenetic radiation spewed out of the robots' out of every pore. In retrospect, I was probably violating FCC regulations every time I turned it on, and people driving by probalby just heard "KSSSSHHHHHHH" on their radios. Needless to say I had considerable difficulty getting a clean signal through a contact mic; it was mostly hum. I ordered every single comercially available mic and built every DIY one I could find on the internet. None of them could withstand the hum, and furthermore, most had very poor bass response, making them unsuitable for the spectral analysis I was doing in my research. So I went on a quest to design a contact mic that could withstand massive hum and had good bass response, so I could complete my dissertation. The result is Marshmallow. It is the best contact Mic I have heard, so I decided to share it!