Category Archives: Electronics

Fast and Efficient Pitch Detection: Bitstream Autocorrelation

      DSP, Electronics, Pitch Detection, Software

So, since last year, I’ve been mulling over a unique, and extremely fast(!) Autocorrelation scheme for monophonic pitch detection. Last weekend, I finally got myself to write the proof of concept. It’s not like any autocorrelation scheme I’ve seen before. I am still wondering why no one has thought about doing it this way. As far as I can tell, this is my invention, but please tell me if there’s something I am missing and if I’m not the first to actually do it this way. I dubbed the technique Bitstream Autocorrelation.

Unlike standard Autocorrelation, my scheme works on single bit binary data streams instead of floating point (or fixed point) real numbers. Compared to standard Autocorrelation, Bitstream Autocorrelation is wicked fast. As I’ve been working on multiple channels of audio on small Microcontrollers, I’ve consistently shied away from Autocorrelation schemes for pitch detection (see my original article: Fast and Efficient Pitch Detection). Popular time-domain Autocorrelation (ACF)  based pitch detection, including variants such as AMDF (Average Magnitude Difference Function), ASDF (Average Squared Difference Function),  YIN, and MPM,  are quite expensive in terms of CPU cycles required (ACF is basically an N² operation for N samples).

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The Last of the XRs

      Evolution, Pickups, Uncategorized, XR Series, XR Update

Almost immediately after I announced our Roadmap for 2018, the XRs and the current Nu modules went out of stock as people hurriedly grabbed what’s remaining in our inventory. I am very sorry that I had to turn down orders after the stocks were depleted.

Dan Rhodes sent me these nice pictures of his electric with Cycfi XR dual pickups, Cycfi Resonant Filter, Warmoth body and neck with a Decoboom pick guard, Fender locking tuners, roller bearing nut and Wilkinson tremolo.

“Looks and sounds amazing Joel! I spent some time with it last night and the tonal range of these pickups is amazing. The openness with the tone and Q maxed out is a sound I’ve never had before.”

Thank you very much for such nice appreciation. I am missing the XRs already!

But watch out. We are still actively pursuing the Modula, a new breed of pickups and the next evolutionary step for the XR. It didn’t die, it simply evolved! 🙂

Modula 8 and 9 String Prototypes

      Evolution, Modula, Pickups

So many things to do. So little time! I think Karl Steinberg was right in remarking that I have too many projects happening all at the same time. Oh well, these Modula prototypes are good to go. We worked so hard for this. These are custom made pickups. We do not have injection molded enclosures yet, so these are hand crafted, painted and buffed to perfection. This is already the third version, but it was all worth it! The next, and the most stressful step: Production!

Modula is our next gen, full-range pickups. Leave a comment if you are interested in these pickups!

8-String, 3-5 split Stereo Modula Pickups

9-String, 4-5 split Stereo Modula Pickups

9-String, 4-5 split Mono Modula, Nu Combo

Fast and Efficient Pitch Detection: Double Trouble

      DSP, Electronics, Infinity, Pitch Detection, Software

This D string was driving my pitch detector nuts. It’s jumping from fundamental to octave and back all over the place. Can’t make up its mind! The effect is like a wacko version of Satch with a whammy pedal gone haywire.

What the hell am I talking about? Last month, I wrote about a fast and efficient software multichannel pitch detection scheme using dual peak-detectors. I needed it to be as efficient as possible, so I can run multiple detectors simultaneously using a small 32 bit microcontroller (MCU). Most of the time, it works really well, except in some cases, like that troublesome D string.

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Modula Update: Magnetics

      Electronics, Modula, Pickups

I find it amusing when people talk about the “sound” of the magnet in pickups :-). The magnet has no sound! If you don’t believe me, perhaps you might reconsider if it’s coming from Bill Lawrence. Here’s what he has to say on the matter:

When I read that ceramic magnets sound harsh and alnico magnets sound sweet, I ask myself, ” Who the hell preaches such nonsense?” There are harsh-sounding pickups with alnico magnets and sweet-sounding pickups with ceramic magnets and vice-versa! A magnet by itself has no sound, and as a part of a pickup, the magnet is simply the source to provide the magnetic field for the strings. The important factor is the design of a magnetic circuit which establishes what magnet to use.

It does not really matter which magnet you use as long as the magnetic circuit is properly designed within sensible parameters. One design consideration is the total magnetic pull the magnets exert on the strings. Too strong, and you’ll get “stratitis” (No, it’s not some kind of ailment amongst guitar players ;-). Another important factor is magnetic flux variance versus distance, following the inverse square law. Simply put, magnetic pull decreases as the square of the distance from the magnet. Hence, the choice of magnet may influence the string displacement as it vibrates over the magnetic field.

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Modula Update: Preamp Performance Tweaks

      Electronics, Evolution, Modula

I can’t recall how many times we went back to the drawing board. Design, test, rinse repeat. I only wish turnaround time is shorter than it is now. After initial design, planning, and breadboarding, we start off with dead bug prototyping and do a barrage of tests to validate the design. Then, we do PCB layout using Eagle CAD (although we might be switching to KiCAD soon) and send the design to PCB manufacturing. A cycle takes around 1 to 2 weeks depending on complexity. PCB layout itself can be a demanding task, especially if space constrained, like the Modula preamplifier. What’s painful is when you are in the final stages, and there’s that yet one more test that breaks to design! It happens! And it happened again with the Modula preamp.

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Modula Update: Nice Little Coils

      Electronics, Modula, Pickups

Nice and clean! I just got a set of sample coils straight from the manufacturer and so we got excited and assembled these guys into the Modula’s dual coil profile. With that profile (bobbin-less, 1000 turns per coil, gauge 44 at 4mm width), the coils are very difficult to wind using our home-grown pickup winding machine. Our early attempts were good enough for prototyping and one-offs, but I had to ask our favorite coil factory to do it for us for production.

So how does it sound? That’s what excites me most! I did a quick listen. The sound is very close to the XR, but with an even tighter response, having a very small aperture. Snappy, with lots of sweet harmonics, yet balanced from low to high frequencies. I think this can be a perfect general purpose pickup for a host of instruments. More on that soon!

Modula Update: The Preamp

      Electronics, Modula, Support Electronics

Look what we have here! It’s the Modula Preamp. It’s a balanced design using the ADA4084 Low Noise, Rail-to-Rail Input/Output, Low Power Operational Amplifiers, with a 625μA supply current per channel and 3.9 nV/√Hz noise density. The Op Amp can go up to 36 volts (imagine the headroom)! But for practicality, 9-18v ought to be enough. Hey, this is a rail-to-rail amplifier, meaning the output can swing to the full supply range without clipping. I can’t even imagine driving a guitar amplifier with 9v peak to peak, but you can if you want to, and if your strings can generate that much oomph. Perhaps the bass guitar can? Yet, if your battery is running low, it can still work down to 3v!

After at least 5 revisions, this is so far, the best small preamp we can come up with. This guy went through a long incubation period (tests, tests and more tests!), until we finally settled on a design that I really like. I’ll share some test results soon.

The design is modular too! This preamp is reusable. You have balanced inputs —headers at the top for +in, -in and ground, and single-ended output, plus supply —headers at the bottom for out, ground and supply.

The preamp assembly connects to the S-shaped Modula adaptor board and which can accommodate mono or stereo (using two Modula preamps). Stereo Modulas allow for split pickup configuration (See A New Breed of Pickups).