Stable Micro Systems - Model Acoustic Envelope Detector -Acoustic Energy Analysis Tool for Assessing Food Quality

The Acoustic Envelope Detector is an instrument that measures the acoustic energy released by a sample as it is being deformed by the Texture Analyser (Plus models only) and, in conjunction with Exponent Connect software, converts and displays this in decibels (dB) – the standard measurement of sound. Acoustic emissions, in the audible range up to a frequency of 12.5kHz, are detected close to the sample using a microphone and pre-amplifier from Danish sound and vibration experts Brüel & Kjær which has high sensitivity to the frequencies emitted by brittle products, but has low sensitivity to mechanical noise emitted by the Texture Analyser. This information is converted from an analogue signal (voltage) that represents the total acoustic energy released from the product as it varies with time. This voltage is measured while the TA.XTplusC and TA.HDplusC Texture Analyser simultaneously measures the force, distance and time to provide the4th dimension in texture analysis.

See tests being performed in Exponent Connect software

In addition, Exponent Connect software can now process audio and synchronise this data as .wav files. The audio files (.wav files) recorded through the Acoustic Envelope Detector are useful for several purposes:

• The audio files greatly aid comprehension when analysing test results. Being able to hear the audio while seeing the audio data and Acoustic Envelope data helps the user to understand the nature of the data they are analysing.
• Keeping the audio files from your tests allows a better comparison between different acoustic environments. One laboratory may have different background noise to another laboratory, and listening to the actual audio may allow you to easily identify this.
• When analysing the test results, listening to the .wav files allows you to immediately hear whether there were unwanted background noises that have polluted your test data.
• When setting up acoustic tests to compare products against previously stored test data, the ability to HEAR the test environment is useful to ensure the environment is acoustically similar.
• When used with the Video Capture System the RAED Module provides the audio to accompany the video footage. The user then has Force, Video, Audio and Envelope data that may be studied together to provide a full understanding of the interaction between forces and noise produced from the breaking of a sample.

The measurement of sound

Acoustic data is measured and displayed in Exponent Connect software in real time alongside mechanical measurements (force, distance and time) to identify certain events during a test, e.g. the popping sound when a beverage can is opened or the break of a biscuit as it is snapped. This sound measurement provides another dimension of quantitative data on fractures or audible events that occur when a sample is deformed during testing.

Perhaps the most salient characteristic of crunchy and crispy foods is the sound emitted upon their disintegration/fracture during chewing or in mechanical testing. When a crisp food is broken or crushed they invariably have a jagged stress-strain relationship. In addition, characteristic sounds are produced due to, for example, the brittle fracture of the cell walls of fruits or vegetables or the fracture of individual layers within a matrix product such as a crisp biscuit.

Sensory ‘crunchiness’ and ‘crispness’ are perceptions of not only force-deformation-time events but also, and almost certainly primarily, of their acoustic effects. It has been found, in fact, that the combination of acoustic and mechanical techniques more adequately describes food sensory perception than either technique alone.

The sound emitted from a product becomes its characteristic ‘acoustic signature’. The Acoustic Envelope Detector provides a tool for the quantification of this sound emission whilst measuring the textural properties of the product.

The marketing of sound

Advertisers use onomatopoeia so consumers will remember their products – words for things are created from representations of the sounds these objects make. In the past few years, advertisers have made use of the crispness and crunchiness of foods. Television viewers cannot experience the taste or the smell of a product being advertised. They can only see it and, of course, hear it. Advertising the aural assets of a food acquaints the potential customer with this most important quality attribute of many products. Consumers then associate ‘acoustic signatures’ with various products which enhances their appeal, success and brand loyalty.

The application of sound measurement

Whilst much work in this area has focussed on measuring crispness of brittle foods like breakfast cereals, or potato chips or the crunch of a chewing gum tablet coating or fresh apple, potential applications include the quantification of::

• The ‘snap’ of a cracker/biscuit/chocolate bar (whilst measuring its breaking strength)
• The ‘pop’ of a cork (whilst measuring its ease of removal)
• The ‘fizz’ of a bath bomb or disintegrating tablet (whilst measuring its firmness)
• The ‘snap’ of a pencil (whilst measuring its breaking strength)
• The ‘click’ of a switch (whilst measuring its actuation force)
• The ‘crack’ of a Christmas cracker (whilst measuring its pull strength)
• The ‘zip’ of a zipper (whilst measuring its pull strength)