Tag Archive for: enhanced Loose particles

A New Method for Transient Distortion Detection

Transient distortion, or ‘loose particle’ measurement, is an important loudspeaker production line quality control metric that identifies and facilitates troubleshooting of manufacturing issues.

This paper introduces a new enhanced loose particle measurement technique that discriminates more accurately and reliably than current methods. This new method introduces ‘prominence’ after envelope detection, a new metric for audio measurements, that effectively isolates transient distortion in the presence of periodic distortion. This technique also offers the unique ability to listen to the isolated transient distortion waveform which makes it easier to set limits based on audibility and has widespread applications.

Authors: Steve Temme, Rahul Shakya and Jayant Datta, Listen, Inc.
Presented at 155th AES Conference (October 2023) New York, NY

Full Paper

 

Paper Introduction

Transient distortion, or ‘loose particle’ measurement, is a valuable quality control metric because it identifies non-periodic distortion, for example, rattling parts, separately from periodic distortion such as rubbing or buzzing parts. This facilitates troubleshooting of manufacturing issues. This paper introduces a new transient distortion measurement technique that is more accurate and reliable than current methods. In addition to improved performance, this new algorithm also aids understanding of the correlation between measurement results and audibility, since it is possible to isolate and listen to just the transient distortion artifacts. Although this analysis method was developed for measuring loose particles in loudspeaker drivers, it is also valuable for measuring rattling parts such as buttons, fasteners, and loose wires on various audio devices, and measuring impulsive distortion or Buzz, Squeak and Rattle (BSR) in automotive audio applications [1].

What is Transient Distortion? Why does it matter?

Transient distortion is caused by random clicking, popping, and other noises in the time domain. In a speaker or headphone driver, this might be caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap. In a device such as a smart speaker, transient distortion might come from a loose volume control button on the device that rattles when sound is played. In an automotive application, it could be characterized as buzz, squeak and rattle from loose wires, screws or fasteners in a car door that the loudspeaker is mounted in. In all cases, the sound is undesirable, so devices that exhibit such faults should be identified and rejected.

In the recorded time waveform, transient distortion faults appear as impulsive noises added on the stimulus wave. These impulses are not related to the frequency of the stimulus, but rather to the vibration caused by the displacement amplitude of the diaphragm. The transient distortion is more frequent and significant when the speaker is driven near or below its resonant frequency, where the displacement of the diaphragm is the greatest.

Although the sound – a random clicking, buzzing or popping noise – can sometimes sound similar to higher order harmonic distortion (Rub & Buzz), such defects are not clearly reflected in the frequency spectrum of the waveform. Figure 1 shows a waveform with transient distortion, and the corresponding frequency spectrum. The vertical black line represents the stimulus frequency and the orange broadband noise spectrum indicates the transient distortion. Transient distortion is best identified at the time the transients occur, unlike Rub & Buzz distortion which is best identified by the frequency at which it occurs [3].

The entire paper also covers:

Prior Measurement Methods

The new algorithm – comparison and results

Conclusions

Download paper

In addition to this paper, please also check out the Enhanced Loose Particles Webpage and our detailed video explanation of how this algorithm works.

New Transient Distortion Measurement Algorithm

At Listen, we’re at the forefront of audio measurement research, and we’re always looking to improve on existing audio measurement techniques, even our own! Loose Particle detection has been a valuable production metric for analyzing transient distortion since we launched it in 2004. This new iteration uses our own original research to improve accuracy and reliability, show a clear correlation to audibility, and simplify limit setting. In addition to production line testing of speakers, headphones, drivers and other devices, it is also valuable for automotive Buzz, Squeak and rattle (BSR) measurements and measuring rattling components such as keys and buttons on a variety of devices. All is explained in the short video below.

Transient Distortion Detection Launch Video

Watch our launch video (broadcast date 05/25/2023) for the full details.

 

Ready to Measure your Transient Distortion?

If you have SoundCheck 21, you already have this new algorithm! Download our free complete end of line test sequence with enhanced Loose Particles to start using it right away.

If you don’t have SoundCheck 21, but have an older version, you can send us your recorded waveforms and we’ll analyze them for you and send you the results. Please contact sales@listeninc.com for a test sequence to record the waveforms.

No SoundCheck system at all? No problem! You can send us your speakers and we’ll test them for you. Or we may be able to arrange a system loan. Contact your sales engineer at sales@listeninc.com for more information.

Prefer to Read About It?

We know not everyone has 15 mins free to watch a video, although its hard to beat the benefits of a proper demonstration. So here’s a brief summary of the information about this new algorithm that is presented in the video:

What it does

The new algorithm measures transient distortion caused by loose particles that may become trapped in a device during manufacture and create an unpleasant sound when they vibrate in the finished product. This is measured in the time domain rather than the frequency domain as these artifacts appear randomly over time, and not periodically in the same way that harmonic distortion artifacts are presented. This algorithm has a couple of unique features:

1) It measures transient distortion separately from harmonic distortion which gives deeper insight into the failure mode and accelerates troubleshooting, particularly on the production line.

2) It’s easy to correlate with audibility as the algorithm removes the stimulus waveform to allow the user to listen to just the distortion artifacts. As well as enabling the user to truly understand how measured results correlate to listening, this also facilitates limit setting.

3) It’s reliable even in the presence of transient background noise since it relies on a cumulative event count rather than a single event triggering a fail. Limit setting is simple as it is not frequency dependent

 

Applications

  • Production line driver test
  • Production line finished product test (rattling buttons, keys, grills, and other components)
  • Buzz, Squeak and Rattle (BSR) / Impulsive distortion measurements in cars

 

How it works

Like Listen’s original 2004 transient distortion detection algorithm, enhanced Loose Particles relies on a time domain analysis of the waveform. However, rather than simply filtering and counting transients, it removed the stimulus, performs a time domain analysis of the remaining transients, then applies a unique Prominence calculation to evaluate each transient in the context of the surrounding waveform. A threshold is applied, and the number of transient events above that threshold are counted. The event count indicates whether a device has a transient distortion problem. Transient events caused by speaker manufacturing issues tend to repeat many times as particles bounce around in side the speaker, or components vibrate. In contrast, background noise events occur infrequently during the duration of the measurement. The threshold is set based on audibility, and the Loose Particle count limit can be set according to the environment to fine-tune the algorithm for the specific operating conditions.

 

Graphic demonstrating how the Transient Distortion algorithm (Loose Particles) works

4 Stages of the enhanced Loose Particles algorithm for transient distortion measurement: Response waveform, Loose Particle waveform, Prominence and enhanced Loose Particles.

 

 

For additional background, comparison to other methods, such as Crest Factor Analysis, and live demonstrations, please check out the video above.

 

Learn More

100 Things #15: Loose Particle Detection for Identifying Transducer Manufacturing Defects

Loose Particle Detection is a technique for analyzing random transient distortion in the time domain. It is an important measurement for end of line transducer QC as it identifies manufacturing defects caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap. This algorithm This differs from Rub & Buzz measurements which analyze the higher order harmonics in the frequency domain to detect periodic distortion.

Note: This video was made in 2022 and highlights Listen’s original Loose Particle Algorithm. This was updated in the 2023 release of SoundCheck (Version 21) to the new Enhanced Loose Particle Algorithm. While the principal of time-domain analysis remains, the new algorithm utilizes a new metric, Prominence, to offer results that better correlate to audibility. Check out the information on the new algorithm listed in the links below.

Loose Particle Detection for Transient Distortion Analysis

Learn more about SoundCheck’s Loose Particles (transient distortion) analysis

Watch the new 100 Things video introducing the updated 2023 version of this algorithm.

Watch the video introduction to Enhanced Loose Particles – Listen’s newest Loose Particle Detection Algorithm.

Read about the Enhanced Loose Particles algorithm.

Read the AES paper published about this new algorithm for transient distortion detection.

 

Video Script: Loose Particle Detection for Identifying Transducer Manufacturing Defects

SoundCheck’s unique Loose Particle Detection Algorithm analyzes random transient distortion in the time domain. This identifies manufacturing defects caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap –  otherwise known as ‘crap in the gap’. Although this algorithm has been in SoundCheck since 2005, I’m always surprised how few people are aware of it, since it’s so valuable for improving manufacturing yield.

Let’s first look at the types of distortion we see on the production line. Conventional Rub & Buzz measurements analyze periodic distortion by looking at higher order harmonics in the frequency domain. These usually indicate a rubbing voicecoil or similar. However, with loose particles, analysis in the frequency domain does not yield useful information.

Loose particle analysis examines transient distortion in the time domain. This identifies random clicking, popping or rattling noises made by particles trapped behind the diaphragm or dust cap.  We can visualize this by looking at both the time and frequency analysis of the signal together. Here, in the frequency domain, you can see the periodic distortion, in other words, Rub & Buzz. And here, in the time domain, you can see the random transients, or loose particles.

Let’s take a closer look at the algorithm.

Loose particle detection uses a swept sine stimulus and time-envelope analysis of the waveform response to capture the transients. Detection thresholds are set for the magnitude, duration, and number of transients to quantify their level and number over time. Limits and filters are applied to separate device transients from background noise. Fine tuning with these tools customizes the algorithm for your product and manufacturing environment.

Measuring the different types of distortion enables rapid troubleshooting and correction of manufacturing problems, and SoundCheck is the only production line measurement system that can accurately distinguish between periodic and random transients.

Loose particle detection is also useful for identifying loose or rattling components such buttons, keyboards, wires and fasteners. In the digital domain, it can catch Bluetooth dropouts, clipping and other digital signal processing artifacts. This functionality is available in all editions of SoundCheck – check it out!