Olfft1 and Fetchfft

This document describes two programs, OLFFT1 and FETCHFFT, developed for the PDP-12 computer to perform on-line frequency analysis of neurophysiological data (such as EEG).

• OLFFT1 is designed to transform one to four channels of continuous analog data into their respective power spectra in real-time. It uses the Fast Fourier Transform (FFT) algorithm, samples data via a real-time clock, removes the mean (DC) value to prevent signal swamping, and stores the resulting spectra on magnetic tape for later analysis.
• FETCHFFT is the complementary program used to retrieve, display, and plot the spectra previously stored by OLFFT1. It provides options for viewing data (including a logarithmic scale), printing specific frequency amplitudes, and generating hard-copy plots of the spectra.

The system requires a PDP-12 with 8K memory, a KW12 real-time clock, and analog-to-digital converters. The documentation includes detailed instructions on operation, scaling factors, hardware configuration, memory usage, and common pitfalls such as aliasing.