Blue Ribbon Microphone

Edmund_Lowe_fsa_8b06653If you’ve ever seen an old movie or TV show where there was a radio announcer, you’ve probably seen a ribbon microphone. The RCA 44 (see Edmund Lowe, on right) had exceptional sound quality and are still valued today in certain applications. The name ribbon microphone is because the sound pickup is literally a thin strip of aluminum or other conductive material.

Unlike other common microphones, ribbons pick up high frequencies much better due to the high resonant frequency of the metallic ribbon. This is not only better in general, but it means the ribbon mic has a flatter frequency response even at lower frequencies. Another unique feature is that the microphone is bidirectional, hearing sounds from the front or back equally well. It is possible to build them with other directional patterns, although you rarely see that in practice.


In the early 1920s, Walter Schottky and Erwin Gerlach developed the ribbon microphone (and, coincidentally, the first ribbon loudspeaker). Harry Olson at RCA developed a ribbon mic that used coils and permanent magnets which led to the RCA Photophone Type PB-31 in 1931. Because of their superior audio response, they were instant hits and Radio City Music Hall started using the PB-31 in 1932. A newer version appeared in 1933, the 44A, which reduced reverberation.

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A Pi Powered Recording Studio

In the mid-90s, you recorded your band’s demo on a Tascam cassette tape deck. These surprisingly cheap four-track portable studios were just low tech enough to lend an air of authenticity to a band that calls itself, ‘something like Pearl Jam, but with a piano’. These tape decks disappeared a decade later, just like your dreams of being a rock star, replaced with portable digital recording studios.

The Raspberry Pi exists, the Linux audio stack is in much better shape than it was ten years ago, and now it’s possible to build your own standalone recording studio. That’s exactly what [Daniel] is doing for our Raspberry Pi Zero contest, and somewhat predictably he’s calling it the piStudio.

Although the technology has moved from cassette tapes to CompactFlash cards to hard drives, the design of these four-track mini recording studios hasn’t really changed since their introduction in the 1980s. There are four channels, each with a fader, balance, EQ, and a line in and XLR jack. There are master controls, a few VU meters, and if the technology is digital, a pair of MIDI jacks. Since [Daniel] is using a Raspberry Pi for this project, he threw in an LCD for a great user interface.

As with all digital recorders, the money is in the analog to digital converters. [Daniel] is using a 24-bit, 216kHz, four-channel chip, Texas Instruments’ PCM4204. That’s more than enough to confuse the ears of an audiophile, although that much data will require a hard drive. Good thing there will be SATA.

Although you can buy an eight-channel solid state recorder for a few hundred dollars – and [Daniel] will assuredly put more than that into this project, it’s a great application of a ubiquitous Linux computer for a device that’s very, very useful.


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Aquire Awesome Audio for BeagleBone

[Henrik Langer] put his powerful audio acquisition and output board up on, and we thought we’d point it out to you. It’s one of those projects that used to be pro audio just a few years back, but is doable (and affordable) DIY today: dual stereo inputs and four(!) stereo outputs, all sampled at 24 bits and up to 192 kHz. It’s configured as a BeagleBone cape, and comes with a customized Linux distribution for the ‘Bone.

What would you do with such a thing? It’s essentially a recording studio in your pocket, with a computer attached. The video (linked below the break) demonstrates using the device as a real-time stereo delay effect unit, but that’s only making use of one channel. Between effects, recording, and then all sorts of much-better-than-CD quality sound synthesis and playback possibilities, it’s an open-ended audio playground.

And all that from what is essentially a (very well-done) breakout board for a fancy DAC/ADC chip from Analog Devices: the AD1938. We’d love to have one of these on our desktop. Check out [Henrik]’s GitHub for the PCB and build instructions and BOM and everything else you’d need to get started. Very nice job!

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Tape Loop Echo Made With an Actual Tape Loop

A lot of digital processes are named after an old analog device that they’ve since replaced. It’s not uncommon to “tape” a show nowadays, for example, even though the recording work is actually done by a digital video recorder. Sometimes, though, the old analog devices have a certain je ne sais quoi that is desirable even in today’s digital world. This is certainly the case with [Dima]’s tape loop echo which is actually made with a physical tape loop.

The process of building the tape loop hardware is surprisingly non-technical. By positioning a recording head and a playback head right next to one another, a delay is introduced. An echo is created by mixing the original live sound signal with this delayed signal coming from the tape By varying the speed of the tape or altering several other variables, many different-sounding effects can be achieved.

Although in practice it’s not as simple as it sounds (the device required a lot of trial-and-error), the resulting effect is one that Pink Floyd or Beck would surely be proud of. Analog isn’t the only way to go though, there are plenty of digital effects that are easily created, and some with interesting mounting options as well.

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Make a Microphone Out of a Hard Drive

[Rulof Maker] has a penchant for making nifty projects out of old electronics. The one that has caught our eye is  a microphone made from parts of an old hard drive. The drive’s arm and magnet were set aside while  the aluminum base was diagonally cut into two pieces.  One piece was later used to reassemble the hard drive’s magnet and arm onto a wooden platform.

v2_micThe drive’s arm and voice coil actuator are the key parts of this project. It was modified with a metal extension so that a paper cone cut from an audio speaker could be attached, an idea used in microphone projects we’ve previously featured. Copper wire scavenged from the speaker was then soldered to voice coil on the arm as well as an audio jack. In the first version of the Hard Drive Microphone, the arm is held upright with a pair of springs and vibrates when the cone catches sound.

While the microphone worked, [Rulof] saw room for improvement. In the second version, he replaced the mechanical springs with magnets to keep the arm aloft. One pair was glued to the sides of the base, while another pair recovered from an old optical drive was affixed to the arm. He fabricated a larger paper cone and added a pop filter made out of pantyhose for good measure. The higher sound quality is definitely noticeable. If you are interested in more of [Rulof’s] projects, check out his YouTube channel.

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DIY Bass Drum Microphone Uses Woofer Cone As Diaphragm

Anyone into audio recording knows that recording drums is a serious pain. Mic setup and positioning can make or break a recording session. One particular hurdle is getting a great sound out of the bass drum. To overcome this, [Mike] has built a microphone using an 8″ woofer in an attempt to capture the low-end frequencies of his bass drum. Using a speaker as a microphone isn’t a new idea and these large diaphragm bass drum mics have taken commercial form as the DW Moon Mic and the now-discontinued Yamaha SubKick.

The project is actually quite simple. The speaker’s positive terminal is connected to Pin 2 of a 3-pin XLR microphone connector. The speaker’s negative terminal is connected to the connector’s Pin 1. [Mike] made a bracket to connect the woofer to a mic stand, which in turn was cut down to position the woofer at bass drum height. The setup is then plugged into a mixer or pre-amp just like any other regular microphone.

[Mike] has since made some changes to his mic configuration. It was putting out way too hot of a signal to the preamp so he added an attenuation circuit between the speaker and XLR connector. Next, he came across an old 10″ tom shell and decided to transplant his speaker-microphone from the open-air metal rack to the aesthetically pleasing drum shell. Check out [Mike’s] project page for some before and after audio samples.

Adding stereo to monophonic audio


A lot of awesome stuff happened up in [Bruce Land]’s lab at Cornell this last semester. Three students – [Pat], [Ed], and [Hanna] put in hours of work to come up with a few algorithms that are able to simulate stereo audio with monophonic sound. It’s enough work for three semesters of [Dr. Land]’s ECE 5030 class, and while it’s impossible to truly appreciate this project with a YouTube video, we’re assuming it’s an awesome piece of work.

The first part of the team’s project was to gather data about how the human ear hears in 3D space. To do this, they mounted microphones in a team member’s ear, sat them down on a rotating stool, and played a series of clicks. Tons of MATLAB later, the team had an average of how their team member’s heads heard sound. Basically, they created an algorithm of how binarual recording works.

To prove their algorithm worked, the team took a piece of music, squashed it down to mono, and played it through an MSP430 microcontroller. With a good pair of headphones, they’re able to virtually place the music in a stereo space.

The video below covers the basics of their build but because of the limitations of [Bruce]’s camera and YouTube you won’t be able to experience the team’s virtual stereo for yourself. You can, however, put on a pair of headphones and listen to this, a good example of what can be done with this sort of setup.

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