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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, without also picking up sounds traveling 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 several, 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. Metal Marshmallow Youtube Playlist

Features

• 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 soldered 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 20 mm tall. The entire length, including the audio cable 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

Details about how I measured this are on my blog.

Anatomy

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 about one hour, after which it will stay charged for about 10 days before it needs to be charged again, 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.

Charging

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. It is possible to use the microphone while it is charging but you may observe some extra noise at 16 kHz which can be filtered out. Please note that Metal Marhsmallow does not come with a charger or USB cable, you have to supply your own.

Tech Specs

	Metal Marshmallow
Gain	14dB (white), 24dB (red), 33dB (black)
Housing Color	Silver
Housing Material	Milled Aluminum
Housing Diameter	39mm
Housing Height	20mm
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

Variations

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
	GREEN	1.0x	+0 dB
	WHITE	4.7x	+14 dB
	RED	15x	+24 dB
	BLACK	47x	+33 dB

Plug It In

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!

Contact

Please contact me with any questions or concerns at michael.krzyzaniak@yahoo.com