Tag Archive for: 100 things

100 Things #97: Zwicker Loudness Measurement

Zwicker Loudness Measurement, an indication of overall perceived loudness level, is calculated in SoundCheck using the Zwicker Loudness post processing step. Instead of just measuring the absolute sound pressure level in dB SPL relative to 20uPa, the Zwicker Loudness algorithm takes into account how humans hear sound level using  the PEAQ international standard. This is an ITU-developed standardized algorithm for objectively measuring perceived audio quality as subjects would in a listening test.

Zwicker Loudness Measurement

Learn More About SoundCheck’s Advanced Features

Read more about more measurement features in SoundCheck.

More information is also available in the  SoundCheck Manual.

 

Video Script: Zwicker Loudness Measurement

Did you know that SoundCheck can calculate the overall perceived loudness level using a Zwicker Loudness post processing step ? Instead of just measuring the absolute sound pressure level in dB SPL relative to 20uPa, the Zwicker Loudness algorithm takes into account how humans hear sound level using  the PEAQ international standard. This is an ITU-developed standardized algorithm for objectively measuring perceived audio quality as subjects would in a listening test.

The input to this post processing step must be a spectrum of a complex signal in pascals or dBSPL. We can easily capture this in SoundCheck using an FFT or RTA broadband measurement using a calibrated Reference Mic signal path. To simulate the non-linearity of the ear, the Zwicker Loudness algorithm then filters these frequencies into auditory bands according to the bark scale – a frequency scale where equal distances correspond with perception. Once the spectrum is plotted on a bark scale, a frequency weighting is applied that correlates to human hearing. Finally, a level compression is applied and the loudness is output in Phons and Sones. The loudness spectrum can optionally be shown with the X axis either in Hertz or Bark.

Knowing the actual perceived loudness of a signal is extremely important for certain applications. For example, listeners that are trying to subjectively compare different headphones will be biased towards the louder one. If I want users to subjectively compare two different headphones, I need to make sure they are played back at the same level to avoid this bias. Looking at the 1kHz sensitivity of each headphone doesn’t take into account the difference in frequency response across the two devices. Often A-weighting is used to correlate measurements to human hearing, but a simple A-weighting curve makes a lot of assumptions such as what level of playback that will be used. Zwicker Loudness gives us a much more accurate perceived loudness, and enables us to precisely match the loudness, in phons, between the two devices regardless of level..

Zwicker Loudness is also widely used in communication testing for measuring loudness of both speech transmission, and ringtones. Check out our website to learn more.

 

100 Things #96: Laser Displacement Measurement of a Loudspeaker

Laser displacement measurement is a technique for measuring the peak displacement of a loudspeaker diaphragm at various power levels, frequencies or both. Did you know that SoundCheck can easily be configured to include a laser signal path? This makes it easy to correlate diaphragm displacement with electrical impedance and audio artifacts. In this short video, we demonstrate laser displacement measurements of a loudspeaker.

Laser Displacement Measurement

Get Our Free Laser Displacement Measurement Test Sequence

Ready to try it for yourself? You can read more and download this laser displacement measurement sequence here.

More information on configuring SoundCheck for use with lasers is also available in the  SoundCheck Manual.

 

Video Script: Laser Displacement Measurement of a Loudspeaker

Displacement lasers can be used to measure the peak displacement of a loudspeaker diaphragm at various power levels, frequencies or both. Did you know that SoundCheck can easily be configured to include a laser signal path? This makes it easy to correlate diaphragm displacement with electrical impedance and audio artifacts. Let’s take a look.

First, we create a Laser Signal Path in Calibration and once that’s done, a new calibrated device file for the instrument.  The sensitivity of most lasers is expressed in Volts per Millimeter and in this case, our laser’s sensitivity is 100 volts per millimeter.  After creating custom units, we can enter the sensitivity value, select a hardware channel and we’re ready to measure!

In this sequence, we’re using a stepped sine sweep starting at 1 kHz and ending at 20 Hz, and  we’re also simultaneously measuring the impedance and frequency response of our speaker under test.  The recorded time waveform from the laser can be analyzed just like any other waveform but there’s one additional post processing step required after analysis, converting the displacement level from RMS to peak.

As you can see, configuring SoundCheck for laser measurements couldn’t be easier. The resulting data can be used to study the displacement of the speaker under test and can even be used in conjunction with other SoundCheck measurements to calculate more advanced metrics such as Thiele-Small parameters. You can learn more about advanced speaker measurements on our website, www.listeninc.com.

 

100 Things #92: Continuous Log Sweep with Time Selective Response Analysis

Did you know that SoundCheck was the first audio test system to implement the continuous log sweep stimulus, way back in 2001. Also known as a frequency log sweep, or Farina sweep, this stimulus is used with time selective response (TSR) analysis. TSR analysis allows reflections to be windowed out, making it great for loudspeaker simulated free field measurements and room acoustics measurements. It’s also valuable as a smart trigger for robust open loop measurement testing. Watch this video for a quick overview.

Continuous Log Sweep with Time Selective Response Analysis

Learn more

Read on about stimulus and analysis capabilities in SoundCheck.

 

Learn more about Simulated Free Field Measurements

Short Video Demonstration of free field measurements without an anechoic chamber

Full-length Demonstration of free field measurements without an anechoic chamber

Article explaining simulated free field measurements (reprinted from Voice Coil Magazine)

The Original 1992 paper introducing the Simulated Free Field Measurement Technique

 

Learn more about room acoustics measurements using the Log Sweep Stimulus

Full-length Demonstration of Room Acoustics measurements

 

Video Script:

Did you know that SoundCheck was the first audio test system to implement a continuous log sweep stimulus? We introduced it back in 2001,  shortly after Angelo Farina’s landmark AES paper on the subject. Let’s take a look at how it works and how it’s used.

A continuous log sweep, sometimes known as a frequency Log sweep or Farina sweep,  is a continuous sine sweep with equal time and energy in every octave. Since it sweeps slower at low frequencies but speeds up as the frequency increases,  it’s a great choice for fast measurements. It differs from a conventional stepped sine stimulus, in that the continuous log sweep plays across all frequencies in the range with a defined sweep rate per decade, whereas the stepped sine sweep “steps” through different frequencies across the range.

Both stimuli can measure frequency response and harmonic distortion, but the analysis methods differ. A continuous log sweep uses a time selective response, or TSR analysis. This involves calculating an impulse response and applying a user-defined time window that can isolate or  remove any reflections caused by the test environment. A stepped sine requires a HarmonicTrak analysis. Only the continuous log sweep with TSR analysis can window out reflections, allowing a simulated free field measurement even when you are not in a fully anechoic environment.

Let’s take a look. In the TSR analysis step, we’ll enable this checkbox here to output an impulse response to the memory list so we can view it. It can be displayed either on a linear or logarithmic scale.  The window size at the top is where we define the start and stop points of the window that’s applied to the impulse response. We can look at this in SoundCheck to help us decide which points to use. Here, we can clearly see a large impulse that has been autodelayed to 0 seconds to show the direct sound from our sound source. And because we’re in a non anechoic environment, just a normal room, you can see reflections from the walls, floor, ceiling, table etcetera.  in the impulse response. We can adjust the window to remove them, and you can see the frequency response updates. 

This technique is very powerful, but like all techniques there are tradeoffs. So Log TSR analysis might not be the best option for all applications. The measurement resolution is affected by the window size – as the window size narrows,  the frequency resolution reduces, and you can see the effects on the frequency response. This is particularly noticeable at the lower frequencies where  the lack of resolution can make the data inaccurate if the window is too small. We need to be careful to configure the window size to capture the direct sound but be wide enough to get the greatest frequency resolution, without any reflections due to the test environment.

TSR Analysis  offers significant benefits for several applications. We use it for the high frequency measurements in a loudspeaker simulated free field measurement, which we can then splice together with the low frequency Stepped Sine Sweep stimulus measurement. It’s also valuable for room acoustics, for example, for calculating RT60 and clarity measurements. And if you’re running open loop tests, our cross-correlation smart trigger uses a continuous log sweep to provide a way of triggering an open loop measurement that is extremely robust and far less susceptible to false triggers than other methods. 

To learn more about the applications of a continuous log sweep stimulus, check out the technical papers and demo videos on our website.

100 Things #91: Measurement of Intermodulation Distortion

Intermodulation Distortion measurements are a great alternative to harmonic distortion for measuring narrowband devices such as hearing aids and communication devices. In such devices, harmonic distortion measurements tend to underestimate the distortion as the higher-order harmonics fall outside the pass band of the device. In this short video, Steve Temme demonstrates and explains the two IM distortion measurement options in SoundCheck – intermodulation distortion and frequency distortion and discusses how they can be used for low frequency speaker measurements, narrowband devices and microphones.

Measurement of Intermodulation Distortion

Learn more

Read on about more analysis capabilities in SoundCheck.

Video Script:

Although harmonic distortion is perhaps the most commonly measured distortion metric, it’s often not ideal for measuring narrowband devices such as hearing aids and communication devices. These products often have a high frequency cut-off around 3-5 KHz, so the higher-order harmonics fall outside the pass band of the device, so harmonic distortion measurements often underestimate the distortion.

A useful alternative we offer in SoundCheck is intermodulation distortion. Intermodulation distortion relies on the interactions between two simultaneous pure tones to produce measurable intermodulation products. These measurements actually present a more realistic representation of real-world signals such as speech and music that are rich with intermodulation products than the single tone used in harmonic distortion

SoundCheck offers two intermodulation distortion measurement options – Intermodulation Distortion and Difference Frequency Distortion. For Intermodulation Distortion, we superimpose a sweeping frequency tone against a fixed frequency tone. For Difference Frequency measurements, we use a stimulus consisting of two sweeping tones separated by a specified frequency interval, which can be a fixed difference or a fixed ratio. These are fully customizable.

In both cases, the two signals interact to produce intermodulation products. With Intermodulation Distortion, these are equal to the sum and difference of the upper frequency and integer multiples of the lower frequency. Difference Frequency distortion, only considers the components that are the difference and multiples of the difference, between the excitation frequencies.

Each type has its own specific applications. For example, Intermodulation distortion is mostly used for loudspeaker measurements, particularly at low frequencies, and Difference Frequency distortion is ideal for testing narrowband devices as the frequencies can be chosen so that the intermodulation products mostly fall within the pass band. This is easy to do in SoundCheck – simply configure your two test stimuli, and select your analysis – either Intermodulation Distortion, or Difference Frequency Distortion – in the analysis editor.

Intermodulation distortion is also a valuable technique for measuring microphones. Usually, the harmonic distortion from the source speaker playing the test tone is greater than the harmonic distortion that you are trying to measure from the microphone. However, if separate test tones are fed individually to two separate loudspeakers, the loudspeaker’s harmonic distortion has no influence on the measured intermodulation frequency components, enabling accurate measurement of the microphone’s intermodulation distortion.

To learn more about intermodulation and other types of distortion, check out our website, and stay tuned for a new in-depth seminar on distortion.

100 Things #73: Active Speech Level Control in SoundCheck

SoundCheck’s incorporation of active speech level allows for stimulus to conform with telephony testing standards. This means testing to IEEE and TIA standards can be automated within a sequence, allowing an entire test to be run without operator intervention. Active speech level is incorporated directly into SoundCheck’s stimulus step, and becomes available when selecting dB RMS. Active speech level can also be used for setting voice activation levels or wake word testing for smart devices.

Active Speech Level Control in SoundCheck

Learn more about active speech level in SoundCheck

Our Telephones application page details all of the benefits of using SoundCheck to test your communications devices.

Video Script:

Did you know that SoundCheck offers Active Speech level control in both the stimulus editor and post-processing?

Many telephony standards such as IEEE and TIA specify speech stimulus levels in terms of active speech level, or ASL.  It can also be used for setting voice activation levels or wake word testing for smart devices.

When active speech level is used, signal levels are scaled using only the parts of the waveform where speech is actually present, rather than the overall RMS level. Silent gaps are excluded but utterances that are part of normal speech are included. This removes variability due to different speaking speeds and content when making measurements, and provides better consistency for standardized measurements.

Configuring ASL in SoundCheck is easy. Let’s take a look.

If you’re testing with speech, you’ll be loading a speech file as a WAV file stimulus. Simply select the file, or open it from the memory list. In the level drop-down, select dB RMS and this will enable the ASL checkbox. Make sure the ASL checkbox is selected, and set the level of your stimulus. 

ASL is also available as a post-processing step. Here, you have some additional parameters. You can adjust the Time Constant  – that’s the time constant of the exponential averaging used to measure the level of active speech . You can modify the Hangover Time – that’s the allowable time for silence between utterances, 200ms is the default. And you can also set the Margin  – that’s the  difference between threshold of activity and the active speech level. This is useful because if the background noise is high, you can reduce the margin to exclude the noise. 

When you are using Active speech level in post-processing, The ASL value in the Memory List displays the Percentage of time during the waveform where speech is active, the mean power of speech measured over the aggregate time of activity and the mean power of the waveform measured over its entire duration.

Active Speech Level is an optional module, and can be added to any SoundCheck system.

100 Things #71: Calculating Thiele-Small Parameters of a Loudspeaker

SoundCheck can be used for loudspeaker design, performing measurements of loudspeaker performance in an enclosure, known as Thiele-Small parameters. SoundCheck includes three different methods for calculating Thiele-Small parameters: known mass, added mass, and known volume. Depending on what driver measurements are known and unknown, these three sequences provide options for all testing scenarios. Operator messages steps are included in all sequences, making testing a wide variety of devices easy with one sequence.

Calculating Thiele-Small Parameters of a Loudspeaker

Try it Yourself

You can try these sequences for yourself! Check out all three Thiele-Small Parameter test sequences in our sequence library, where you can download them free of charge and try them on your own SoundCheck system.

Learn more about Thiele-Small Parameters

Listen founder and president Steve Temme, and support manager Steve Tatarunis, co-wrote a technical article on practical impedance measurement. The paper dives into both single channel and dual channel measurement methods, considerations, techniques, measuring thiele-small parameters, and more.

Video Script:

Thiele-Small (T/S) Parameters define the mechanical, electrical and electromechanical properties of a loudspeaker and predict how a driver will work in an enclosure. It’s a common measurement for loudspeaker designers, and it’s easy to do in SoundCheck. 

SoundCheck offers 3 built-in methods for calculating the Thiele-Small parameters – known mass, added mass, and known volume. You can also use a laser, but that’s a subject for another video. Let’s take a look.

The ‘known mass’ method is when the mass of the driver is known along with the effective cone diameter and coil resistance. The sequence begins with user prompts to enter all three of these. Next a stepped sine sweep is used to calculate the impedance of the loudspeaker.  A series of post processing steps uses this curve and the data entered by the user to generate the Thiele-Small Parameters, which are displayed on two tables.

Thiele-Small parameters can also be measured when the mass of the driver is not known. In this case, we use the ‘added mass’ method. First the user is prompted to enter the driver diameter and a stepped sweep is run to calculate the impedance curve without the added mass attached.

Next the user can either enter the DC Resistance of the loudspeaker or use the minimum impedance method.  Using minimum impedance involves searching for the lowest value of the impedance curve.  Now, we enter the value of the added mass in grams and attach it to the loudspeaker. This added mass can be modeling clay or mounting putty stuck to the cone close to the voice coil to change the resonant frequency of the loudspeaker. Another stepped sweep is run and a second impedance curve is calculated.  A series of post processing steps uses the data entered and measured to generate the Thiele-Small Parameters in two tables.

The third method, known volume, assumes we know the total volume of the enclosure. In this case, we enter the driver diameter and we make an impedance measurement using a stepped stweep with the driver mounted vertically in free air. Like before, we can enter the DC Resistance of the loudspeaker or use the minimum impedance method.The second impedance measurement is made with the driver mounted in the known volume and a series of post processing steps uses the measured and user-input data to generate the Thiele-Small Parameters.

If you already have SoundCheck, you can download test sequences for all 3 methods from our website – check it out!

100 Things #37: Pre-written Test Sequences for Measurements to Audio Industry Standards

We offer a whole catalogue of pre-written SoundCheck test sequences to save you development time when testing to audio industry standards. Written by industry professionals in each field, these sequences cover a variety of devices and applications including headphones, communications devices, loudspeakers and more.

Pre-written Test Sequences for Measurements to Audio Industry Standards

Learn More About Test Sequences for measuring to industry standards

Check out our video and free test sequence for testing to AES75 (M-Noise) Measurement of Max SPL for Loudspeakers.

See our selection of for-purchase SoundCheck sequences for testing to standards.

 

Video Script: Pre-written Test Sequences for Measurements to Industry Standards

Did you know that in addition to our multitude of free resources and test sequences, Listen offers a library of “for purchase” test sequences that conform to a variety of industry standards?

Our hearing aid test package tests to the ANSI S3.22 and IEC 60318-7 standards while the EN 50332 sequence provides assurance that headphones and music players meet the Max Noise Exposure criteria set in the standard.  Other packages include calibration of a 4.1 speaker array for background noise simulation to ETSI ES 202 396-1 and measuring volume control requirements for wireless mobile devices as set forth in TIA 5050. We also offer various sequence packages for testing telephones, speaker phones and headsets to various other telecommunications standards including IEEE 1329-1999, TIA-920-B, and Doubletalk to both ITU-T P.502 and ETSI TS 126 132 standards.

Each Sequence package comes with a schematic diagram of the required hardware setup, detailed instructions for setting up your hardware, Hardware editor, calibration editor and related test hardware, and a general overview of the sequence.

Visit our website to learn more.

 

Welcome to 100 Things You Didn’t Know About SoundCheck

In this video, Steve Temme, Listen’s founder and president, introduces our new video series ‘100 Things You Didn’t Know About SoundCheck’. This series of 100 videos highlights some of SoundCheck’s best-kept secrets – innovations, algorithms, analysis techniques and more that you may not know about.

Welcome to 100 Things You Didn’t Know About SoundCheck

Learn More About Our Audio Test System

SoundCheck Main Page.

Check out the latest new features in SoundCheck.

See our Innovation Timeline – a historical run-down of the major innovations in SoundCheck.

 

Video Script: Welcome to 100 Things You Didn’t Know About SoundCheck

Hello, my name is Steve Temme, founder and President of Listen, Inc. I’d like to introduce you to our new video series 100 Things You Didn’t Know About SoundCheck.

Since I started Listen back in 1995, our software-based audio measurement system, SoundCheck, has constantly evolved, expanding its capabilities with each new release. We’ve also introduced many hardware products to complement the software and meet increasingly complex test requirements.

The challenge of such a long history is that it’s hard to effectively share all of the vast functionality. I’ve lost count of the number of times customers have commented on some capability they’d love us to include, only for me to share with them that we have been able to do that since the 1990s or early 2000s! For example, I was recently asked whether we could offer a log chirp stimulus since one of our competitors recently implemented it. We’ve had it since 2001! – in fact we were the first commercial audio measurement systems to use it!

Anyway, that brings me to the purpose of this video series. Over the next one hundred short videos we’ll highlight some of SoundCheck’s best-kept secrets –  innovations, algorithms, analysis techniques and more that you may not know about. Some of these features have been around for decades, while others have been more recently added. Join us in this video series as we show you why sound measurements make sound products.