I am a software developer and audio recordist, who enjoys designing and building audio equipment and measuring instruments. Follow the links below to find out what I've been up to:
I recently gave a talk at SDiOS about implementing an AC impedance bridge using the sound hardware in your iPhone, or other compatible device. My slides and XCode projects are available here for download.
All the functionality of the S-Domain Bode/Nyquist Plot Java applet is now available in the Z-Domain. Most of you will have to build and run the applet from source, due to the new security restrictions surrounding Java applets. In this case, I would say it's well worth the effort.
A major upgrade to my original Bode Plot Applet, lets you set the start frequency, choose units for the horizontal axis, view a Nyquist plot of your transfer function, and estimate the impulse and step function responses. As with the original version, the focus remains on cascading multiple filter sections to obtain the desired transfer function. Complete source code is available for download.
When testing software parsers it helps to have a large library of test cases which are valid inputs for the parser. A comprehensive test strategy should include both constructed test cases, designed to address specific requirements, and randon test cases, meant to generally stress the parser and following steps. Presented here is a technique which generates random valid test cases by populating a composite tree structure with randomly chosen operators and operands. Simple examples are given in a variety of computer languages, along with complete source code for you to build and run the examples.
To accurately reproduce the signal from a musical instrument pickup, one must reduce loading on the pickup as much as possible. This means increasing the input impedance seen by the pickup to very high levels. I present here a technique which reduces loading by connecting to the instrument with triaxial cable. The inner shield is actively driven to further reduce input capacitance.
A "Measurement Appliance" is simply a measuring instrument which exposes a file system interface. This is my definition, which I'm using to promote a new paradigm for data acquisition, measurement, and control. Posted at this link is my manifesto for the development of measurement appliances, which I believe will be an enabling technology for future developments in measurement and test.
A new topology for audio oscillators is introduced, which is reminiscent of the familiar Wien Bridge oscillator. A detailed schematic is given for a tone generator that runs on as little as 1.5 Vdc using the Sallen-Key configuration. The tone generator is then used to implement a phantom-powered signal source for testing balanced microphone inputs.
Online supplement to my article "Design and Measurement of a Dipole Microphone", in the June 2009 issue of audioXpress magazine. In it, I predict the performance of a directional microphone using an Excel spreadsheet. I then implement the design in a prototype, and verify performance with a gated tone burst measurement technique.
Online supplement to my article "Balanced Cable Hum: Cause and Cure", in the May 2009 issue of audioXpress magazine. In it, I describe the problem of 60 Hz hum induced into balanced-line microphone cables.
Java applet written to draw the Harrison construction of free electron Fermi surfaces for a 2-D square lattice. User can vary number of electrons per unit cell, and how many zone boundaries to show. Java source code posted for free download, using the Java 1.1 event model.
Online calculator to obtain molar ratio and gram ratio of precursors required to obtain a desired result. Includes database of atomic weights. Allows any number of precursors and results. Optimized for solid-state chemistry.
Java Animation is easy when you use an affine transformation matrix, but Java 1.0 doesn't have this transform built in. I've implemented my own affine transform using only Java 1.0 classes and methods in a Java applet I call "CrankShaft." Follow this link to see if it works in your browser.
I've been using digital audio technology to record my musician friends. Presented is a list of my equipment, as well as some notes on what works and what doesn't.
Complete construction details and characteristics of an improved active direct box for musical instruments. Mic and line outputs are provided, and it can run on battery or phantom power. This design lets you put the input stage where it counts, on your instrument, by mounting a small circuit board inside a 1/4" phone plug.
Try out my Java Applet for plotting the gain and phase response of continuous time active filters. Supports analysis of cascaded filter sections by multiplying polynomials and collecting terms. Updated to improve cross-platform compatibility. Complete source code is available for download.
In 1958, Frank Lloyd Wright designed a cottage to be built near the Wisconsin Dells for a young computer programmer named Seth Peterson. I recently spent several days at the cottage, and took some snap shots for your enjoyment.
Now I've done it! And just when you thought Analog Computers had finally been laid to rest. Presented here are complete plans for a general purpose audio oscillator which achieves excellent performance with the use of analog computing techniques.
Access online, updated information about my article "Notch Filter Design" in the ONE:2000 issue of Audio Electronics magazine. For schematic diagrams and an Excel spreadsheet, see the topic State Variable Filter Design, below.
Find out how resistance changes with temperature in copper wire. Download a spreadsheet with calculations and figures from my article "Loudspeaker Failure Modes" in the TWO:1999 issue of Speaker Builder magazine.
Learn how to design active filters. Download a spreadsheet which plots frequency response, before you build. Two canonical forms are shown, with simulation diagrams and schematics for each.
Musical instrument pickups typically sound better when working into a very high impedance input. Shown is the schematic for my original Active Plug prototype with 5 MegOhm input impedance and 1 KOhm output impedance, low enough to drive long cable runs at mic or line level.
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