Reference frequency for third octave filters

A DATS user asked…

We are using the third octave band filter at very low frequencies (~1Hz)  and I noticed that the response of the filter could introduce very significant errors for short or transient signals. Looking a bit more in details at the function, the help says:

“For audio work ISO standards use a reference frequency of 1kHz not 1Hz”

Does that implies that for non-audio work, a reference frequency of 1Hz should be applied? If yes, is it possible to change this reference frequency in the dats function?

Dr Mercer replied…

Essentially there is no problem and no need to change the reference frequency provided you use Base 10 mode and not Base 2. Base 10 is the ANSI S1.11-2004 preferred scheme. (more…)

Continue ReadingReference frequency for third octave filters

There are tachometer signals available on the vehicle CAN-bus. Can I use these signals instead of connecting my own tachometer signal?

A simple question should have a simple answer and that answer is “No”.

As usual, however, life is never that simple. (more…)

Continue ReadingThere are tachometer signals available on the vehicle CAN-bus. Can I use these signals instead of connecting my own tachometer signal?

What is Source Contribution Analysis (or SCA)?

How do you measure the causes of a noise or vibration with respect to several sources? Which source is causing what part of the response?

For example, how does the noise inside the cabin of a vehicle relate to the engine noise or wheel hub noise and vibration? (more…)

Continue ReadingWhat is Source Contribution Analysis (or SCA)?

What is the difference between Operating Deflection Shapes (ODS) and Operational Modal Analysis (OMA)?

ODS = Motion of structure vibrating naturally (for example bridge vibration) or when excited by an unknown force (for example generator vibration). Prosig’s Structural Animation software performs ODS analysis.

OMA = Modal Analysis
Prosig’s Modal Analysis software performs OMA. (more…)

Continue ReadingWhat is the difference between Operating Deflection Shapes (ODS) and Operational Modal Analysis (OMA)?

What is the difference between Transfer Path Analysis (TPA) and Source Contribution Analysis (SCA)?

Transfer Path Analysis (TPA) provides the route of the noise or vibration through the structure, not just which sources cause the response, but the route taken. This is useful for developing and improving components like engine anti-vibration mountings or suspension anti-vibration mountings. (more…)

Continue ReadingWhat is the difference between Transfer Path Analysis (TPA) and Source Contribution Analysis (SCA)?
Read more about the article Wide Band Integrators – What Are They?

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 the frequency increases. As a result of this, integration using Omega arithmetic has been prevalent by using Fourier Transforms of the signal. This, of course, remains a valid approach and is particularly useful if the data is already in the frequency domain, which was its prime purpose.

Continue ReadingWide Band Integrators – What Are They?
Read more about the article What is Synchronous (Angular) Sampling?

What is Synchronous (Angular) Sampling?

The 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 spaced time intervals. The rotating part could be an engine, a gear wheel, a drive shaft, a turbine rotor, a propeller, a turbocharger or any other type of rotary mechanical device. Typically these items are subjected to out-of-balance forces that cause them to vibrate at frequencies that are multiples of the fundamental (once per revolution) rotation speed frequency. (more…)

Continue ReadingWhat is Synchronous (Angular) Sampling?
Read more about the article Understanding Filter Characteristics

Understanding Filter Characteristics

Recently when discussing with an engineering student the characteristics of filters, it became clear that some confusion exists around this subject area. This note attempts to explain the differences between types of filter and the effects of the parameters of those filters. (more…)

Continue ReadingUnderstanding Filter Characteristics