Wavetable Synthesis Simplified

I developed a presentation as part of my Sprockit workshop. I think it’s a pretty clear presentation of wavetable synthesis and that it clearly shows how aliasing happens and how to avoid it. I’ve often found that it is difficult to find this type of clear and simple explanation of fundamental synthesis concepts that is particularly useful for the DIY Synth community. So, click through for some learning…

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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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Wave-soldering SMT Components

I’ve been having some issues lately with wave-soldering lately.  Component manufacturers are starting to discontinue some through-hole package parts, forcing many of us into surface mount.  You would think that everybody is using surface mount technology in this new millennium but there are some powerful reasons that many of us dwell in the electronic stone age.

Surface mount designs often end up being designed on double-sided boards.   Double-sided boards cost more than twice as much as single sided circuit boards and, in these Walmart days, cost is king.  If you’re going to do a single-sided board and you’re working in power electronics, some of your components are going to be through-hole parts no matter what you do.  Caps and power devices like MOSFETs require size and volume to either provide sufficient capacitance or to dissipate heat.  If you’re going to mix surface mount devices with through-hole devices, you’re either going to hand-place a lot of your through-hole components after placing your SMT parts, or you’re going to glue your SMT parts down, insert all your through-hole stuff and pass the whole thing through the wave.  There are many considerations to passing SMT parts through a wave-soldering process.  I found an excellent summary of things you need to consider.

http://www.ami.ac.uk/courses/topics/0170_wsp/index.html

Wave-soldering some surface mount parts is never going to work. You can’t easily wave-solder QFPs or QFNs and you’ll never wave-solder a BGA.  If you stick to SOIC packages, it’s possible if you follow the suggestions in the link, particularly part orientation and thieving pads.  I’ve had some success on some seriously high volume (we’re talking millions) designs.