FFT Archive
What is Synchronous (Angular) Sampling?
Posted on November 9, 2011 | No CommentsThe term synchronous data is usually applied to vibration or acoustic data that is captured from an item of rotating equipment at regularly spaced angle intervals as distinct from regularly...
Video: Noise & Vibration From Rotating Machines
Posted on October 4, 2011 | No CommentsThis is complete version of the video illustrating my recent article How To Measure Noise & Vibration In Rotating Machines. This video was previously published on the blog in 3 parts....
Understanding Windowing And Overlapping Analysis
Posted on August 30, 2011 | 2 CommentsThe following article was inspired by a question asked by a reader regarding my previous article - Data Windows : What, why and when?. Specifically, the reader asked “Could you please...
Amplitude And Energy Correction – A Brief Summary
Posted on September 1, 2009 | 8 CommentsAmplitude and energy correction has been and is a continuing point of confusion for many people calculating spectra from time domain signals using Fourier transform methods. The first thing to...
Data Windows : What, why and when?
Posted on July 20, 2009 | 7 CommentsBefore we discuss the use of data windows, we should first remind ourselves of three basic properties of the FFT (Fast Fourier Transform) process. First, energy information in signal must...
10 Great Fourier Transform Links
Posted on April 22, 2009 | 7 CommentsFollowing a discussion in the office about Fourier Transforms we did a little searching on the web. As always, we discovered that the Internet is packed with some great resources...
Sound Steering
Posted on September 12, 2007 | No CommentsThe requirement was to develop a ‘standard’ test for assessing the sound quality of power steering pumps in vehicles. Measurements needed to be objective so that the method would be...
Order Cuts And Overall Level
Posted on February 25, 2007 | No CommentsOrder cuts are taken from a set of FFTs, each one at a different rpm. The rms level is then found as the Square root of the Sum of the...Average Waterfalls Or Average Orders?
Posted on June 14, 2005 | No CommentsOne would expect that averaging waterfalls and then extracting orders would give the same result as extracting orders from individual waterfalls and then averaging them. This is not the case.
Notes On Fourier Analysis
Posted on July 29, 2003 | 14 CommentsFourier analysis takes a signal and represents it either as a series of cosines (real part) and sines (imaginary part) or as a cosine with phase (modulus and phase form)....Frequency, Hertz & Orders
Posted on February 3, 2002 | No CommentsThe most common form of digitising data is to use a regular time based method. That is data is sampled at a constant rate specified as a number of samples/second....
Understanding The Cross Correlation Function
Posted on June 6, 2001 | 3 CommentsTo illustrate the use of the cross correlation function, a source location example is shown below. For this it is assumed there is a noise source at some unknown position...
Data Decimation. What Do I Do?
Posted on June 6, 2001 | No CommentsSometimes we have digitised data at a much higher rate than we need. How can we reduce the sampling rate? If I wanted to say halve the sample rate can...
