Echo And Reverb In A Pretty Little Box

These days, if there’s a chip worth using, there will be a cheap pre-built module on eBay to make using it even easier. It’s a great time saver, and projects that used to take a couple of weekends can now be completed in a rainy afternoon. [lonesoulsurfer] knows how it is, and took advantage of this very approach to build this tidy echo & reverb effects box.

The build starts with a PT2399 echo/delay line module sourced of eBay, a part that we’ve learned much about thanks to the hard work of others. A resistor is cut off the board, enabling echo as well as reverb functionality. It’s laced up in a box with a couple of pots and a switch to control the effect, and hooked up with 6.5mm audio jacks to enable it to be easily used with guitars, synths, or karaoke machines.

It’s a fun build, and one that could serve as as a useful component in a larger setup. Adding a 3PDT switch could make it more useful as a guitar pedal, or it could be integrated into a Eurorack module, too. We’d particularly love to see the results possible from stuffing five of the modules in a single box and routing them into each other in new and exciting ways. If you pull that off, drop us a line.

C++ Reverbs From A Matlab Design

The guitar ‘Toing’ sound from the ’70s was epic, and for the first time listener it was enough to get a bunch of people hooked to the likes of Aerosmith. Reverb units were all the rage back then, and for his DSP class project, [nebk] creates a reverb filter using Matlab and ports it to C++.

Digital reverb was introduced around the 1960s by Manfred Schroeder and Ben Logan. The system consists of essentially all pass filters that simply add a delay element to the input signal and by clubbing a bunch together and then feeding them to a mixer. The output is then that echoing ‘toing’ that made the ’80s love the guitar so much. [Nebk]’s take on it enlists the help of the Raspberry Pi and C++ to implement the very same thing.

In his writeup, [nebk] goes through the explaining the essentials of a filter implementation in the digital domain and how the cascaded delay units accumulate the delay to become a better sounding system. He also goes on to add an FIR low pass filter to cut off the ringing which was consequent of adding a feedback loop. [nebk] uses Matlab’s filter generation tool for the LP filter which he includes the code for. After testing the design in Simulink, he moves to writing the whole thing in C++ complete with the filter classes that allows reading of audio files and then spitting out ‘reverbed’ audio files out.

The best thing about this project is the fact that [nebk] creates filter class templates for others to play with. It allows those who are playing/working with Matlab to transition to the C++ side with a learning curve that is not as steep as the Himalayas. The project has a lot to learn from and is great for beginners to get their feet wet. The code is available on [GitHub] for those who want to give it a shot and if you are just interested in audio effects on the cheap, be sure to check out the Ikea Reverb Plate that is big and looks awesome.

Build A Plate Reverb From Ikea

Back before we all pirated FruityLoops, before ProTools, and before VSTs and DAWs, audio recording was much, much cooler. Reverbs were entire rooms. Sometimes they were springs. Sometimes, in the high-end music studios, reverbs were plates. These plate reverbs were simply a gigantic sheet of metal mounted in a box about ten feet long, four feet high, and a foot thick. Inside, you had some transducers, some pickups, and not much else. Send a signal into the plate reverb and it will bounce around on this flexible membrane, and  emerge through the output in a suitably reverberant form.

Of course, very few places have a plate reverb anymore because they’re gigantic and expensive and software effects are small and cheap. That doesn’t mean a plate reverb is made of unobtanium. [Leo] just made his own plate reverb out of Ikea shelves and some simple electronics.

This build used an Ikea Bror shelving unit that cost about $50 sans meatballs. The electronics are a surface transducer and two piezo pickups. Total cost was about $100. That’s all that’s needed to put this plate reverb together, but the real trick is making it work as a reverb.

The plate is driven by the audio output of [Leo]’s computer, through a battery-powered amp, and into a transducer. The transducer is then simply placed on the metal shelf. The two piezo pickups are placed on either end of the shelf, with one going to the right channel of one input, the other going to the left channel of the same input. From there, it’s a simple matter of using this Ikea shelf in an effects loop.

From the video below, the setup absolutely works. [Leo] is playing a few drum loops through the reverb, and the results sound like they should. There’s also a neat trick in using a shelf as a reverb; by placing a rag or a cardboard box on the shelf, the reverb is dampened allowing you to ‘mix’ this reverb in real time.

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Circuit Bent Keyboard Is Pretty In Pink

If you’re anything like us, more than a few of your projects were borne out of the fact that you had some crusty bit of gear that was badly in need of a second lease on life. Whether it was a hand-me-down or pulled out of the garbage, we’ve all at one time or another had some piece of hardware in our hands that might not be worth anything in its current form, but would make an awesome excuse for warming up the soldering iron.

That’s what happened when [joekutz] got his hands on this exceptionally juvenile keyboard toy. In its original state, it was so janky it couldn’t even reliably detect two keys being pressed at the same time; sort of a problem for a keyboard. So he decided to pull it apart and use it as a circuit bending playground. Thanks in part to how much free space was inside of the case, he was able to pack in a number of interesting modifications which he’s kindly detailed on Hackaday.io.

[joekutz] started by adding a headphone jack to the device, as well as a switch to disable the keyboard’s speaker. That allows not only listening to digital jams in private, but makes it possible to capture high-quality audio when connected to the computer. He then started poking around the PCB with a resistor and listening for changes. When the pitch of the keyboard changed, he soldered a potentiometer into its place and now had a way to adjust it on the fly.

Of particular note is the clever physical reverb he came up with. A microphone and speaker are connected to each other with a spring made out of an old guitar string. Audio from the keyboard’s PCB is played on the speaker and a TDA2022 low-voltage amplifier boosts the signal from the microphone. The end result is a very cool ethereal metallic effect.

If you’re looking for a slightly larger DIY reverb, we’ve covered a few builds in the past which should give you some inspiration. You might want to check the dumpster behind the abandoned local Toys R’ Us for some donor keyboards while you’re at it.

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Build A DIY Plate Reverb

PlateReverb

[Telegraphy] needed a reverb for his recording studio. There are hundreds of computer-based and standalone digital reverb systems out there, but he decided to build his own plate reverb. Reverb is an effect used in many professional audio and music recordings. Reverb adds thousands of echos to an audio signal. These echos decrease in amplitude over time. When used correctly, the effect is generally very pleasing to the ear.

A plate reverb uses a plate of sheet metal to generate the reverb. An audio driver is placed in contact with the metal plate. Audio is fed into the driver, which vibrates the plate. The vibrations travel along the surface of the plate, bouncing off the edges and reflecting back. These reflections are captured by a pickup, which then converts them to a voltage signal. The final reverb effect is actually created in the sound engineer’s mixing board when the “dry” source signal is mixed with the signal returned by the plate.

[Telegraphy’s] plate reverb was built almost entirely from found, Radio Shack, and hardware store parts. The plate and frame are from Lowes. The audio driver is a cut up speaker from an old car stereo. The pickup is a modified piezo transducer from Radio Shack. As [Telegraphy] states several times, there are a lot of differing opinions on exactly how and where to mount the various parts of the reverb. Any placement will generate some reverb. The question is where and how to mount things for the best effect. Much like beauty and the eye of the beholder, the answer to that question is in the ear of the listener.

Jump past the break for a tour of a slightly more involved plate reverb at Gallery Acoustics Studio.

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DIY Spring And Plate Reverb

If you’re running your own recording studio, you’re going to need a lot of gear that seems excessively esoteric to the non-musically inclined. A rack full of synth gear looks just like any other cabinet of technology you would find in a server room. Electronic music is, for the most part, very utilitarian looking, but there are a few pieces that add a very nice aesthetic touch to any studio. [Peter] made two great looking pieces of hardware – both reverbs – that significantly add to the decor of his studio. As a bonus, they also sound really good.

[Peter]’s spring reverb (Dutch, Google translate) works just the same as any other spring reverb; a speaker puts some music into a slightly stretched spring, and this sound is picked up by another transducer at the opposite end. For this build, [Peter] used a Slinky and a piece of PVC pipe left over from a bathroom remodel. Adding a few jacks, pots, and a preamp, [Peter] had a very nice and extremely large spring reverb.

The plate reverb (translation) is also a staple of pro recording studios around the globe. This reverb is somewhat similar to a spring reverb, except the spring is replaced with a tuned metal plate. [Peter] used a cymbal from a drum set for this piece of kit. Two speakers are attached to the back of the cymbal, one feeds a sound into the cymbal, the other speaker picks up those sounds and sends it to the mixing board.

There’s a lot of really cool musical DIY projects over on [Peter]’s site, along with a few audio demos for each of his DIY projects. We’ve included his reverb demos after the break, feel free to give those a listen.

Thanks go to [geekabit] for sending this one in.

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