Q. Who is ScopeDSP™ for?

A. ScopeDSP is designed for engineers, scientists, and advanced amateurs working in practical applications of Digital Signal Processing. Anybody can use ScopeDSP as a plotting program or for file conversion, but to use all its features effectively you should have an understanding of basic DSP concepts such as complex data, the Discrete Fourier Transform (DFT), data windowing, filtering, and modulation. Most introductory college courses on DSP cover these topics.

Q. What are typical applications of ScopeDSP?

A. ScopeDSP fundamentally is a software tool for analyzing sampled data signals. It began life as a tool to analyze data captured from the A/D (analog-to-digital) converters. Of course, the manufacturer's specifications tell you how well the A/D will perform--if you happen to insert it into the ideal circuit design as they did. Probably your design isn't quite ideal. The process of implementing an A/D converter in a real circuit design and achieving specified performance always involves some iteration. Typically, you will make an initial design, test it, change something in the grounding, shielding, or power supplies, re-test it, and then test it again. To guide your path through this Mysterious High Art, you will need to capture data samples from your A/D into a file and calculate basic some performance specifications such as SINAD and SFDR. ScopeDSP doesn't do the capture part, but it does do the calculation part. See the A/D Performance Measurement tutorial for more details.

Likewise, as you design the rest of your DSP system you probably will simulate it extensively (if you know what's good for you.) But alas, even inside your own seemingly perfect digital Denmark, indeed, something smells rotten. Maybe your software has a bug (say it isn't so!) Or maybe there are spurs or distortion caused by fact that, unlike the textbooks, you chose to implement your DSP system with finite-precision arithmetic. (Tisk, tisk!) ScopeDSP can read and write many data file formats, including the ones used by most of the DSP microprocessor simulators currently available.

Q. How do I acquire a sample from my A/D converter?

A. This is a tough one: the problem of collecting samples from your A/D converter always seems to be a problem. Since ScopeDSP takes its input from files, you must somehow collect data from your A/D and then write it to a file. We can't be of much real help in the capture process; we come in only after you have captured the data as a file. But here are a few tips. One of the handiest ways to capture data, if your A/D is the " parallel" type, is via a Logic Analyzer. Unfortunately, Logic Analyzers are limited to relatively small sample sizes. Some of the newer Logic Analyzers can save data samples on their built-in disk drive (though a disk file format conversion may be required.) Alternatively, you might use an IEEE-488 interface or some other interface to transfer data from the Analyzer to a computer. Of course, if your A/D is connected to a DSP microprocessor and you have an emulator running, you can use that for data capture. Another approach is to buy a "data capture" card that connects to the computer bus of your choice. In any event, be prepared to suffer some aggravation.

Q. How does ScopeDSP handle "real" data (as opposed to "complex" data)?

A. ScopeDSP does all operations internally using complex data. However, just as in the textbooks, "real" data is treated as a special case of complex data in which the "imaginary" signal is zero. For real signals, ScopeDSP just fills the imaginary channel with zeroes.