This week I worked on component selection and the PCB schematic design. As part of this I have worked on both schematic and layout symbols for all of the major parts. Now that I have most of the major symbols done, it will not take much longer to finish the schematic and get the PCB layout done.
In progress schematic:
3D CAD view:
For next week, I hope to have the PCB design finished.
This week I helped in choosing MIDI keyboard for the BOM and continued working on bringup for the FPGA.
We finalized on choosing the MIDI keyboard here : https://www.amazon.com/Alesis-VI25-Controller-Assignable-Production/dp/B00IWVL3SW. This features both a MIDI output as well as the after touch keys and velocity sensitive pads.
Additionally I took last week’s SDRAM tests and started integrating/stripping it down so that we can use the controller independently from the rest of the Altera test files. This is still in progress.
I finished testing writes to the GPIO pins on the FPGA to make sure that we can properly observe the required voltage changes. Below are the results.
Tested using power supplied by laptop (usb)
For the next week I will begin researching more into the Panning effect as well as start writing a simple testbench so we can begin writing verilog for each of the DSP blocks.
This week I was involved in planning for the PCB BOM and research into a couple of the effects we plan on using. For the BOM I first found the official MIDI documention which included some good schematic diagrams that will aid in our PCB design.
After I looked at this for a while I began adding some of the relevant components to our BOM, which included MIDI Cables, Optoisolators, Diodes, and Ferrite Beads.
Outside of this I did some research into information about the actual MIDI protocol and how to implement a Chorus Effect.
I found some good documentation from CMU about the MIDI protocol at this link: https://www.cs.cmu.edu/~music/cmsip/readings/MIDI%20tutorial%20for%20programmers.html .
I learned about the different elements to a MIDI message. One interesting point is that for messages that continue on the same pitch for a long time, they will often omit the STATUS byte and just send a stream of DATA bytes to be more efficient.
For Chorus I learned that there are actually several different elements that you might consider including in a chorus effect. For example sometimes these effects include some sort of pitch shift or amplitude modulation. However since these are effects are separate effects that we plan on implementing on their own I determined that for a chorus effect it would be best to simply use multiple copies of the signal shifted between 0 and 25ms and added together. This is based on some testing in Audacity where I played around with it to determine what sounded good.
This week we’ve been working on laying the framework for our project. To get an MVP we have a few action items:
We hope to finish a few of those items this week.
The PCB and verilog code are being hosted on private github repos. In the verilog repo there is a docs directory which will act as a centralized point for all of our spec files and datasheets.
Individually, here is what we worked on last week:
Roshan has been working on testing the on board SDRAM and other synthesis tasks.
Nick S. has been researching the MIDI protocol and how to implement certain effects.
Nick P. has been working on the PCB/circuit implementation for the project.
ALTERAudio will serve as a compact, feature-rich replacement for effects pedals and and other similar devices which musicians currently use to modify their sounds live. Instead they can utilize their current MIDI controllers in conjuction with an ALTERAudio device to apply several, layered effects to their sound all at once with control over the characteristics of those effects. And best of all is that ALTERAudio’s list of supported effects is expandable since our hardware is re-programmable. With ALTERAudio we’re taking advantage of the underutilized information that comes with every MIDI key-press to make your performance more unique.
Welcome to the ALTERAudio website!
