Tag Archive for: measurements

100 Things #87: Make Non-Coherent Distortion Measurements

Did you know that you’ve been able to make distortion measurements in SoundCheck with real-world signals such as speech and music since 2006? This is a valuable technique for testing modern devices with on-board DSP that filters out signals such as sine waves and noise. Non-coherent distortion measurements offer excellent correlation with perception and are easily implemented in SoundCheck. Steve Temme explains this technique in this short video.

Make Non-Coherent Distortion Measurements

Read more about making non-coherent distortion measurements

The 2006 AES paper on non-coherent distortion measurements is available to read from our technical papers library. This paper details all of the important considerations for making these measurements, including using a multitone versus music for a stimulus signal, understanding distortion measurement results, and more.

Video Script:

We talk a lot about harmonic distortion and transient distortion, but did you know SoundCheck also offers non-coherent distortion measurements? In fact, I believe we were the first audio measurement company to include this option.

Non-coherent distortion is a broadband distortion metric that includes harmonic and intermodulation distortion as well as noise. It offers better correlation to perception than harmonic or intermodulation distortion alone, and it can be used with real-world test signals such as speech and music as long as there is enough energy in the frequency range of interest. Otherwise, you might just be measuring background noise. I usually make these measurements in the nearfield to reduce background noise by placing the microphone close to the loudspeaker. This is particularly useful for the many modern devices that feature DSP that treats pure tones as noise and tries to filter them out.

Non-Coherent Distortion is a normalized cross-correlation measurement that determines the degree to which the system output is linearly related to the system input.

There’s a lot of complex math behind this – if you want to know more about that you can read our 2006 AES paper. Here, I’m just going to show you a quick demonstration.

Configuring non-coherent distortion in SoundCheck is a simple checkbox in the transfer function analysis editor.

I have a good speaker, and a speaker that exhibits some fairly significant distortion. Let’s look at the good speaker first. I’m going to play a short excerpt of Bird On A Wire at 90dB SPL by Jennifer Warnes – this song is widely used as a test track as it has good dynamic range.

And if you look at the results, you can see non-coherent distortion in percent per square root Hertz (spectral density) versus frequency. Since non-coherent distortion uses a broadband test signal for measurement, there is no direct correlation to harmonic or intermodulation distortion in percent. Typically the distortion level appears much lower than harmonic or intermodulation distortion because the test signal energy is spread out over the entire frequency range and not a single frequency for measuring harmonic distortion.

Now I’m going to play the same song on a speaker that I know shows some fairly heavy distortion

Now, looking at these results, you can see the non-coherent distortion is considerably higher than the good unit, especially at low frequencies.

So that’s it. Non-coherent distortion offers a way of measuring transducers with real-world test signals that correlates well to listener perception. To learn more, check out our AES papers on the subject, or download our free test sequence for non-coherent distortion measurement.

100 Things #74: Easily Save Measurements in Any Format

SoundCheck offers flexible options for data processing, allowing measurement data to be saved in a variety of formats. For fast and reliable operation, saving data can be automated with autosave steps in a sequence. SoundCheck can save measurements to a .tdms file for including important metadata with your measurements, Excel for reporting test data and comparing results, text files for lightweight information transfers. and more. All of SoundCheck’s data including waveforms, results, curves, values can be saved in various formats.

Easily Save Measurements in Any Format

Learn more about saving data in different formats in SoundCheck

Learn more about supported data formats in SoundCheck for R&D, Production, and more.

Video Script:

It’s often useful to save your SoundCheck measurement data for statistical analysis, offline post processing, sharing with others, or saving to a database. SoundCheck offers multiple ways to easily save measurement data in many different formats. Let’s take a look!

When you’re running a SoundCheck sequence,  the memory list manages all the data generated. This includes curves, values, limit results and waveforms. This measurement data can be manually saved by right clicking the item in the SoundCheck’s memory list.

Curves, Values and Results can be saved as .dat (SoundCheck’s native binary data format), .txt, .MAT – that’s a MatLab file,  or .TDMS – that’s National Instruments’ structured binary file format. Multiple items can be selected and saved into a single file.

From the WFM tab, waveform data can also be saved directly as .wav, .wfm (SoundCheck’s native waveform), .txt, .MAT and .TDMS.

.TDMS is a new file format supported in SoundCheck 21 and later. TDMS not only supports system and user metadata, but the data is also a fast binary format, minimizing read and write times when a sequence is running. It can also be opened in Excel and Matlab using a converter plugin.

If you use SoundMap, SoundCheck’s time frequency analysis option, you can even save time frequency data directly to a .mat file for further analysis in MATLAB.

Naturally, saving data in a SoundCheck sequence can be automated. An autosave step in your sequence lets you automatically save to any of the formats I just demonstrated, plus an SQL database, and Excel. This makes saving data with each run of your sequence automatic, fast and easy. If you’re familiar with the WATS Test Data Management software, we’ve even developed a utility to convert SoundCheck generated text files directly into WATS for further analytics and process management.

So, as you can see, SoundCheck is supremely flexible when it comes to working with your existing lab or production line workflows, whether you’re someone who likes to run your own calculations and analytics in Matlab or Excel, or when you need fast, automated writing to your own custom database. For more details, check out the instructional videos on saving data in our “Tutorials” playlist.

100 Things #57: Measuring Headphone Active Noise Cancellation in Real Time

Active Noise Cancellation technology is more advanced than ever, and SoundCheck is well-equipped with all the features needed for measuring headphone active noise cancellation. We have a pre-written test sequence to measure all aspects of noise cancellation including passive, active, and total noise attenuation. This sequence is a great fully complete test, or you can use it as a template to expand your test setup to include multiple background noise sources, or add an additional microphone for an even more detailed test of how the ANC circuit responds to dynamic signals.

Measuring Headphone Active Noise Cancellation in Real Time

Try ANC headphone measurements for yourself

Find our free sequence for measuring Noise-Cancelling Headphones here. This sequence first measures the passive attenuation of the headphones, then the active attenuation, and finally calculates the total attenuation.

Video Script:

Did you know you can measure headphone Active Noise Cancellation with SoundCheck, as well as standard acoustic tests such as frequency response and distortion? When measuring noise canceling headphones there are three important measurements to make: passive attenuation, active attenuation, and total attenuation. Passive Attenuation is the amount of noise the headphones block without ANC enabled. Active Attenuation is the amount of noise ANC blocks out. Total Attenuation is the combination of the two measurements.

We even have a pre-written sequence showing off this functionality, called Noise Canceling Headphones, available on our website. You will need a Head and Torso Simulator (HATS) or an acoustic ear simulator with an artificial pinna, at least one speaker for background noise generation, and a set of headphones with ANC.

The first measurement is taken without headphones on the HATS, the unoccluded measurement. The pink noise stimulus is played out of the speakers, and the signal from the HATS is recorded. Next, the sequence pauses while the operator places the headphones on the HATS, then makes the occluded measurement. The sequence again pauses for the operator to enable the headphone’s active noise cancellation, and The third measurement is taken, and the results are calculated.

This test can be modified to work with a diffuse, multi-speaker configuration, and in an environment with two or more speakers, both ears could be measured at the same time. Our new AmpConnect 621 interface has six inputs, and two outputs so you can even measure both the left and right channel simultaneously, while also generating stereo background noise. Using SoundCheck’s new Multichannel RTA, you can measure the acoustic seal  of both the left and right headphone channels simultaneously, and even visualize it in real time. Also, with the Multi-RTA and an external reference measurement microphone positioned immediately next to the outside of the headphone, you can play any complex signal you like out of the source speaker(s) such as real recorded background noise from an airplane and watch in real time how the noise attenuation changes. This is a more realistic representation of how the ANC circuit responds to dynamic signals.  

There are many ways you can modify this sequence, for example, instead of playing out of one source speaker, play out of multiple equalized source speakers to create a more realistic spatial background noise environment. With the new Signal generator’s delay offset feature, this is much easier to do.

How do you measure active noise cancellation? And what are your favorite noise-canceling headphones? Let us know in the comments below! And for more information on all things SoundCheck, head to our website at ListenInc.com.

In-Car Audio Measurements

Screenshot showing in-car audio measurement sequence final display showing frequency response, distortion and Max SPL

Final display of in-car audio measurement sequence showing frequency response, distortion and Max SPL

This in-car audio test sequence measures the transient distortion (also known as buzz, squeak, and rattle, Rub & Buzz, or impulsive distortion), frequency response, and maximum sound pressure level of a vehicle infotainment system to the methods outlined in the Audio Engineering Society Technical Committee on Automotive Audio (TC-AA) in-vehicle measurements draft white paper.  The three measurements are incorporated into one overall test sequence, making it fast and simple to run the entire suite of tests. This sequence facilitates evaluation of the committee’s proposals, and also serves as a basis for any similar in-house measurements. The white paper (linked above) outlines both measurement methods and physical configuration such as microphone and seat positioning in an effort to simplify comparison between vehicles. This test sequence may, of course, be used with your own in-house physical configuration if adherence to the TC-AA guidelines is not essential.

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Advanced Microphone Measurements Part 2

Listen’s Support Manager, Steve Tatarunis, discusses some of the more advanced aspects of microphone measurements. This is an expansion of material covered in the Basic Microphone Testing webinar, and part two of the full advanced microphone measurements seminar. Advanced Microphone Test part 1 shows microphone measurements like polar plotting, open loop, active/passive noise rejection, and more. This seminar is of interest to anyone testing microphone characteristics, both in an R&D and production line environment. The tests featured in this seminar can be used both at component level, whether selecting microphones for devices or component QC, or these tests can be performed on finished products like smartphones, smart speakers, and more.

Seminar topics include:

More advanced aspects of microphone testing including:

  • Phase
  • Open loop microphone testing for voice activated devices such as smart speakers, automotive audio, etc.
  • Intermodulation distortion
  • Advanced hardware and test configurations for measuring microphone arrays
  • Beamforming with broadside and endfire arrays
  • Measuring MEMS devices frequency, sensitivity and power supply rejection (PSR) performance

Presenters: Steve Tatarunis
Duration: 40 Mins

Advanced microphone measurements resources

SoundCheck comes with many pre-written sequences including the sequences demonstrated in this seminar including the microphone test sequences for measuring microphone self noise, microphone substitution, frequency response and sensitivity, and open loop. Additionally, we offer the sequences featured in this seminar measuring digital MEMS microphones and microphone intermodulation distortion in our sequence library for download. Along with the sequences featured in this seminar, our sequence library is full of additional pre-written sequences for basic microphone measurement.

More about advanced microphone measurements

Check out our main page on Microphones, which includes links to test sequences, relevant products and more.

Simulated Free Field Measurements Without an Anechoic Chamber

In this online seminar, Steve Temme explains how to use simulated free field measurements to provide accurate free-field measurements across the entire audible frequency range without an anechoic chamber. This enables measurements that would usually be made in an anechoic chamber to be made in a regular lab or even home office – a valuable capability when so many are currently working from home.

This measurement method, which has been available in SoundCheck since 2001, measures the near-field response at low frequencies and the time-windowed far-field measurement at higher frequencies, and splices them together to provide the response over the entire frequency range.

This seminar explains the acoustics and mathematics behind this method, demonstrates the test procedure with the pre-written (and available free of charge) SoundCheck test sequence, and show how the results correlate to measurements made in an anechoic chamber.

Seminar topics include:

  • Discussion of sound paths and reflections and explaining the mathematic and acoustic principles behind simulated free field measurement techniques
  • Test set-up that can be used to measure this
  • Demonstration of the “Splice” sequence and measurements in SoundCheck
  • Correlation to results made in an anechoic chamber and manufacturer’s published data

Presenters: Steve Temme
Duration: 31 Mins

Resources for simulated free field measurements

Steve Temme and Christopher Struck authored a whitepaper for the AES on simulated free field measurements, available as PDF for further reading.

Our pre-written sequence demonstrated in this seminar for measuring the anechoic response of a loudspeaker without an anechoic chamber, or “Splice” sequence, is available for download from our sequence library

Check out our main page on Loudspeakers and Microspeakers, which includes links to test sequences, relevant products and more.