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About

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.
  • '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 require custom software which is not included).

Features

  • Excellent bass response: Most contact mics have very poor bass-response, giving them a tinny sound. Marshmallow has a built-in preamp that solves this, giving it a full, rich sound.
  • 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. Marshmallow was built with all components in one small package so it can be easily shielded, resulting in a clean, quiet signal.
  • Small physical size: Marshmallow is 30 mm in diameter and 31 mm in height, plus 6 inches of cable and connector. This makes it easy to attach to things.
  • Long battery life:

Anatomy

Images of marshmallow with different parts labelled
  • Piezo Disc: This is the golden metal disk on one end of Marshmallow. It is the 'microphone' part, and should be placed against to the object you want to record.
  • Ground Plate: This is the silver metal disk on the other end of the marshmallow. It is electrically grounded, and helps with shielding.
  • Battery Tray: Marshmallow requires two CR2032 3V watch batteries. They should be placed in the tray with the negative (raised) side resting in the round hole in the tray. The tray should be inserted into Marshmallow such that the negative (raised) side of the battery faces the Ground Plate.
  • Audio Cable: This is standard shielded instrument cable.
  • Audio Connector: This is a standard 1/4 inch mono female receptacle, which accepts a standard instrument cable. Marshmallow can then be plugged into any regular audio interface or mixer.

Getting Started

Install Batteries:

image sequence demonstrating battery installation Marshmallow requires two CR2032 3V watch batteries. To install them, place Marshmallow with the piezo disc facing up. Remove the battery tray. Place both batteries positive (+) side up in the tray, and reinsert the tray into Marshmallow. Please note that these batteries pose a serious choking / ingestion hazard and should be kept away from small children.

Shield:

To make very clean recordings, Marshmallow may optionally be shielded to eliminate hum and other unwanted sounds from the audio signal. This is accomplished as follows:
image demonstrating how to shield Marshmallow by covering it with aluminum foil and tape.
  1. Completely cover the piezo disc and exposed metal surrounding the battery tray with non-conductive tape. Double sided tape is recommended.
  2. Cover all of Marshmallow with aluminum foil, ensuring that it makes good contact with the ground plate. Make sure the foil does not directly touch the piezo disc or the exposed bits of metal surrounding the battery tray, as this could cause a short circuit. Completely covering them in tape will prevent this.
  3. If you are especially paranoid about hum you may also cover the entire audio cable with aluminum foil, and attach it to the audio connector, which is also electrically grounded. This is usually overkill as the cable is already shielded.

Plug Audio In:

image demonstrating how to plug marshmallow into an audio device Use a 1/4 inch instrument (audio) cable to connect marshmallow to your audio interface or mixer.

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!

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