# Author: Dr Colin Mercer

## Is That Tone Significant? – The Prominence Ratio

The Prominence Ratio is a technique designed to see if there are any aurally prominent tones in a signal. Primarily, the prominence ratio is applicable where we have

## A Guide To Digital Filtering

Understanding filters is actually simpler than it may first seem. Creating a filter is another story; it’s like being able to drive a car without having to know

## Wide Band Integrators – What Are They?

For some time now it has been conventional ‘wisdom’ that using time based digital integration may cause amplitude errors in the result and that these get worse as

## Where Does The Noise In A Signal Come From?

When one thinks of noise in a signal, it is generally associated with having been added in some way to the amplitude of a signal.  This is not

## Why is the microphone pressure reference 2*10^-5 Pascals?

This seemingly simple question is actually quite fundamental.  To answer the question we need to consider sound intensity.  Now sound intensity is defined as “the average rate of

## Negative Frequencies – What Are They?

Normally when we are analysing a signal it is a purely real signal, that is it has no imaginary part. A classic example is of course a sine

## Vibration : Measure Acceleration, Velocity or Displacement?

When using vibration data, especially in conjunction with modelling systems, the measured data is often needed as an acceleration, as a velocity and as a displacement. Sometimes different

## Do Missing Tachometer Pulses Mean The End Of The Road For Your Test?

Creating a good quality tachometer signal is one of the hardest parts of analyzing rotating machinery. So what happens if we have missing tachometer pulses? The data looked

## Removing A-Weighting From Time History Signals

It sometimes occurs that signals are captured with A-weighting applied to the data by the acquisition device. This can be a problem if, for example, you wish to

## Aliasing, Orders and Wagon Wheels

These days most people collecting engineering and scientific data digitally have heard of and know of the implications of the sample rate and the highest observable frequency in

## Interpolation Versus Resampling To Increase The Sample Rate

These are two different techniques aimed at different objectives. First consider a simple sinewave that has been sampled close to the Nyquist frequency (sample rate/2). Visually this looks very

## Vibration Monitoring Phase Measurement And The Tacho Signal

Any vibration signal may be analyzed into amplitude and phase as a function of frequency. The phase represents fifty percent of the information so it is most important

## Human Exposure To Vibration In Buildings (DIN 4150-2:1999-06 & DIN 45669-1:1995-06)

Standards DIN 4150-2:1999-06 and DIN 45669-1:1995-06 provide a means of assessing the effect on human beings of vibration caused by vehicle traffic, trains both above and below ground,

## Orders v Time – Comparing Overall Levels

By combining a speed signal with a data signal and using the Short Time FFT algorithm (Hopping FFT), it is possible to extract order data directly as a

## Sound Steering

The requirement was to develop a ‘standard’ test for assessing power steering pump noise (and sound quality) in vehicles. Measurements needed to be objective so that the method

## Order Cuts And Overall Level

Order 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

## Acceleration, Velocity & Displacement Spectra – Omega Arithmetic

Accelerometers are robust, simple to use and readily available transducers. Measuring velocity and displacement directly is not simple. In a laboratory test rig we could use one of

## Examples Of Event Extraction And Removal

In many cases only significant events, such as bumps or other transients in a signal are of relevance. The objective is to be able to isolate these events

## Standard Octave Bands

The “standard” centre frequencies for 1/3 octave bands are based upon the Preferred Numbers. These date from the 19th century when Col. Charles Renard (1849–1905) was given the

## Torsional Vibration, Tacho Pulses And Aliasing

With shafts, gears and the like, the general method of determining the rotational speed is to use some form of tachometer or shaft encoder. These give out a

## Analyzing Shaft Twist And Repairing Damaged Tachos

This post discusses analyzing shaft twist and at the same time handling the less than perfect data that we have all come across. A shaft has been instrumented

## Phase Angle Between Signals

The following article was written in response to a question from a visitor to the website. The gentleman in question had been reading some of the Prosig signal

## Average Waterfalls Or Average Orders?

[latexpage]One 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