Kickstarter Final Countdown + New Video

Hello everyone. Big shout out to all my backers out there. Thank you for all your support over the past couple months. Your messages of support have been instrumental in keeping me focused on the prize. I started this project with the goal in mind of forcing myself to find an ending to this project after about a year and a half of work. And I think I’ve done it.

In the new video, you’ll notice all the work that I’ve put into polishing the design over the past two months. Mostly, I’ve been pounding the hardware. I completely overhauled the final output stage a couple times and spent some good time tweaking the DAC reconstruction filter as well as the main analog filter. The end result of this work has been to massively reduce harmonic distortion and to drop the noise floor way down. Along the way, I found a number of bugs in the code and made huge improvements in the wavetable playback that made aliasing a problem of the past.

Stay tuned after the project ends for details on order fulfillment and my next steps.


Kickstarter Project at 75%

Cheers to you Kickstarter. The project reach 75% funding in only two and a half weeks.

I’ve been through every emotion imaginable. It’s really exciting to reach this point in the project. The response is a validation of the work I’ve done for the past year and a half pretty. I’ve overcome problems which I couldn’t easily resolve after days and weeks of scouring the internet and reading dense textbooks.  I had to learn a lot about digital signal processing, firware optimization, filter design, and about how to use all the parts I ended up using. The good part for you is that I’ve learned about all this stuff, packaged it into the synth, and written about and will continue to write about it on this blog. Click through for more and a celebratory 75% Rockit bassline.

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8 Bit Synth: MATLAB Bandlimited Wavetable Simulation and Aliasing

This is what the MATLAB script outputs. No aliasing here!

I’ve spent a lot of time in the development of the Rockit 8 Bit Synth dealing with aliasing.  I made a MATLAB simulation to get to the heart of the issue visually.  The script simulates the wavetable synthesis process by generating a sawtooth wavetable and playing back that wavetable to generate a 50% duty cycle square wave output. This output is plotted along with the Fast Fourier Transform (the frequency) of the signal  By adjusting some parameters, the amount of aliasing in the signal can be increased or decreased, providing a visual tool for understanding the factors that contribute to aliasing in wavetable synthesis.  Click through for a thorough explanation.

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Bandlimited Wavetable Synthesis

Sin Wavetable
I’ve discussed the phenomenon of aliasing in digital synthesis in several previous posts.  I described the phenomena, it’s source and what it sounds like.  There are many, many solutions to the problem of aliasing in digital synthesis.  A lot of them rely on performing sequences of calculations, multiplications and additions to implement various filtering methods or methods of synthesis which theoretically do not create aliasing, like additive synthesis. In my Rockit 8 Bit Synth, I don’t have the luxury of loads of extra cycles to throw at calculations, so I need something that can reduce the aliasing without requiring boatloads of clock cycles.  I settled on bandlimited wavetable synthesis.  With it, I have reduced the aliasing to a point that I can tolerate and probably further optimize.  Let’s discuss how it works.  Also, click through for source code for generating a wavetable and a sample wavetable from my synthesizer.

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DSP: Aliasing and Synthesis

In a previous post, I discussed how in setting up my oscillators, how I made a proper demonstration of aliasing. I have yet to find a clear description of the problem as it relates to digital synthesis.  There are many sites which define aliasing in engineering terms but don’t make it as easy a thing to understand as it can be.  Follow along as I give it a shot.

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Atavist, where have you been?

LED crazy China

China, naturally. Given that we build almost everything in the world that needs building in China, it’s a pretty natural place for an electrical engineer to end up. I spent two weeks there and another week after I got back recovering from some intestinal parasite. I’m as inclined to blame the airline as I am the delicious food I had in China for the bug that tried to chew it’s way out of my gut.

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