Frequency analysers are very powerful and useful measuring instruments for environmental assessment, source identification, noise and vibration control, machine fault diagnosis and other applications. Frequency analysers measure RF and audio frequency by triggering on events that swept wide range signal analysers fail to see, seamlessly capturing and storing a record of signal activity and enabling in-depth analysis. The RF signals use modulation, frequency hopping, bursting and other techniques and continue to elude swept spectrum analysers. Thus, frequency analysers are abundantly used by designers and researchers to trigger, capture and analyse the spectral behaviour of frequently changing signals. The wide range application of frequency analysers is in environmental noise, environmental vibration, occupational noise and vibration control, personal protective equipment selection, source identification, production line testing of products, machine noise and vibration, commissioning of plant, engineering development and laboratory analysis and education.