Technical Resources
With over 100 combined years of audio measurement experience, our team has created a wealth of technical papers, sequences, articles and other useful information to assist you with your audio test needs. Please browse the collection below, or filter by type of resource.
100 Things #68: Using Transfer Function to Measure Smart Devices
Modern devices are becoming better and better at filtering out unwanted background noise from calls. This includes noises like sine sweeps, typically used to test these devices. Instead testing these devices with real world signals like speech, music, and noise can bypass noise suppression. The ability to use transfer function in SoundCheck to test these devices with non-linear signals was added in 2005. Transfer function can do more than just measure smart speakers, with the ability to also test loudspeaker impedance or compare measurements of a reference mic to a DUT mic, all with the same SoundCheck module.
Using Transfer Function to Measure Smart Devices
Learn more about transfer function, and other SoundCheck features
Read on about SoundCheck features and functionality, discussing algorithms, automation features, and more. If you’re ready to start testing on your own SoundCheck system, see our full catalog of free Loudspeaker test sequences.
Video Script:
Modern devices such as mobile phones, smart speakers, TWS earbuds and audio infotainment systems use sophisticated DSP algorithms to improve the voice quality and intelligibility of these devices. While these algorithms greatly improve the user experience, they create challenges for the audio test engineer as they often filter out common test signals such as sinewaves.
So, if we can’t use sinewaves, then what are our alternatives? SoundCheck’s transfer function algorithm, which was first introduced in Soundcheck back in 2005, can use broadband signals such as speech, music and noise as a stimulus to measure the frequency response of a device.
The transfer function algorithm works in the frequency domain to perform a complex FFT (including magnitude and phase) on the stimulus and response waveforms. From these two spectra, a variety of results can be calculated including frequency response, non-coherent distortion, coherence, non-coherence, signal to noise ratio, cross spectrum, coherent power and non-coherent power. Time domain analysis outputs are also available and include impulse response, auto-correlation of the stimulus and response as well as cross-correlation. A power averaging option can be used when the response waveform contains jitter or other artifacts that would result in phase calculation errors when complex averaging is used. When power averaging is selected, it limits the algorithm’s output to frequency response, auto spectrum of the stimulus and response waveforms and auto-correlation.
Let’s say we want to measure a microphone embedded in a smart speaker which we know uses DSP to filter out sinewaves. We construct a compound stimulus containing the smart speaker’s wake word, Alexa for example, followed by a pink noise stimulus having a minimum bandwidth equal to that of our device under test. When this stimulus is played from SoundCheck, the wake word triggers the smart speaker and its recording of the stimulus playback can be retrieved from the cloud as a WAV file and recalled into SoundCheck for analysis.
Transfer function analysis isn’t limited to just open loop measurements using non-sinusiodal stimuli. We can use transfer function to make high accuracy electrical impedance measurements by measuring the speakers terminal voltage and current or even use the recorded time waveforms of a reference mic and DUT mic to analyze the response of the DUT mic.
In this video, we’ve only scratched the surface of the capabilities of this powerful algorithm. If you’d like to learn more about it, contact one of our sales engineers to arrange a demo. Thanks for watching!
100 Things #67: Measuring Active and Passive Noise Cancellation for Hearing Protection
SoundCheck makes testing to standards simple by automating precise measurements into a single sequence. In this test sequence hearing protection devices can be tested to the ANSI S3.19-1974 standard to find their NRR rating. Sequences in SoundCheck make testing simple, with message steps instructing operators when interaction is needed with removing or placing hearing protection DUTs, for example. ListenInc.com features an extensive list of pre-written test sequences for any application including noise protection devices, hearing aids, bluetooth devices, and more.
Measuring Active and Passive Noise Cancellation for Hearing Protection
Try our hearing protection sequence for yourself
The hearing protection measurement sequence featured in this video is available in our sequence library.
Video Script:
Did you know that you can test hearing protection devices to industry standards using SoundCheck? Let’s take a look.
Hearing protection devices are often measured to the ANSI S3.19-1974 standard which measures the Noise Reduction Rating or NRR of the device. This rating is a numerical representation of the device’s sound attenuation.
Our test sequence first measures the response spectrum of the unoccluded hearing protector test fixture, then makes a second measurement with the hearing protection DUT affixed. SoundCheck’s signal generator generates the pink noise stimulus while its Real Time Analyzer simultaneously records the A and C weighted noise spectrums. The unoccluded and occluded measurements are analyzed with a series of post-processing steps according to the ANSI S3.19-1974 standard. The final display shows the NRR numerical value, RTA spectra of the left and right side of the unoccluded and occluded hearing test fixture, average attenuation level of the DUT, and the standard deviation of the DUT on the test fixture. The sequence prompts the user to recall previously saved unoccluded measurements and standard deviation values, saving time if the test fixture and DUT have been measured previously. When a new unoccluded measurement is taken, the user can save these measurements for a future data recall.
We have many SoundCheck test sequences written by experts to save hours of time writing them yourself. Most of these, including this NRR sequence, are free to use and come with well written step-by-step instructions.
ANSI/CEA 2010-B 2014 Sequence for Subwoofer Maximum SPL
This sequence measures the maximum peak SPL of a subwoofer according to ANSI/CEA 12010-B 2014. In this test, 1/3 octave band limited tone bursts are presented to the subwoofer across a 3 octave range from 20 Hz to 160 Hz. At each frequency, the stimulus level is increased in +3 dB increments until the harmonic (and non-harmonic) distortion and noise (HD+N) exceeds the specified threshold. The level is then decreased by 3 dB and the test continues with level increments of +1 dB until the HD+N threshold is again exceeded. The peak SPL of the fundamental at the last passing test level is recorded and the sequence continues to the next frequency. Peak SPL values are weighted according to the power spectrum defined in the standard and the Average Weighted SPL and final Broadband Peak SPL calculated as specified.
100 Things #66: Quickly Post-Process Multiple Measurements With Average Curves
SoundCheck includes a powerful array of post-processing options, including Average Curves. This step allows for instant averaging of data sets with two averaging options: power and complex. Curve average is perfect for working with data from microphone arrays, making this tool great for automotive and smart device measurement applications, or any device with large microphone arrays. Since SoundCheck is not limited to hardware inputs and outputs, huge measurements can be done simultaneously including up to 64 channels simultaneous acquisition. Once measured, SoundCheck can perform curve averaging to this data even within a sequence.
Quickly Post-Process Multiple Measurements With Average Curves
Try average curves in a sequence
Check out our full library of test sequences. There are sequences for common and specific audio measurement applications, and they make the perfect starting point to add average curve post processing to a sequence.
Video Script:
SoundCheck comes with a lot of great post-processing options and one of my favorites is the Average Curves function which first appeared in SoundCheck 17. This step lets you easily calculate the average of a group of curves and, although the step name doesn’t imply it, it can also be used to calculate the average of a group of waveforms. This is really useful for measuring microphone arrays such as those in automotive infotainment systems and smart devices.
First, we’ll place the data of interest into a Memory List group. Next, we select the group in the step editor’s Operand dropdown. There are two averaging options available; Power and Complex. Power averaging excludes the phase from the calculation and should be used when the curves or waveforms aren’t from the same spatial position, for example when the data has been collected from a microphone array. A group of RTA curves is another example of where power averaging should be used since RTA analysis doesn’t calculate phase. On the other hand, complex averaging should be used when trying to average out random background noise across many repeated measurements of the same device. Here we’ll apply Power Averaging, and you can see the result here.
SoundCheck can capture data from up to 64 microphones simultaneously, so whether the data is coming from multiple microphones, microphone arrays, or even multiple microphone arrays, you can capture the responses and analyze and average the results. Averaging steps can even be incorporated into a test sequence! As microphone arrays become more commonplace in many consumer devices, this measurement has many applications in smart device tests, automotive infotainment measurements, and beyond. How would you use this functionality? Let us know in the comments!
100 Things #65 Save Time With Virtual Instruments Configurations
Since 1997, SoundCheck has had virtual instruments to replace large, heavy hardware instruments. Incorporating these instruments in a software environment means you can utilize all of the benefits of precise digital instruments, with the flexibility of software. For example, limitless combinations of virtual instruments can be opened at one time, then can be saved as a virtual instrument configuration. This options allows for easily re-opening you instruments, and SoundCheck can automate this process and enable instruments to open automatically at startup.
Save Time With Virtual Instrument Configurations
Try virtual instruments
SoundCheck comes with a full library of ready-to-run sequences including a Virtual Instruments sequence. This sequence demonstrates all of the powerful virtual instruments SoundCheck has to offer, and shows how these instruments can be used within a sequence. To learn more about virtual instruments in SoundCheck, check out our page on SoundCheck features and functionality.
Video Script:
Virtual Instruments have been part of SoundCheck since 1997. They replicate the functionality of bench top hardware, for example, signal generators, multimeters, oscilloscopes, etc. within the SoundCheck software. These are great when you need to make an instant measurement, and they’re even better than real hardware as you can also integrate the results with your test sequences.
But did you know that you can simplify your workflow with a startup virtual instrument configuration in SoundCheck? This means that every time you open up your measurement software, your tool bench is configured exactly how you like to use it. All you need to do is create your desired setup and save it. Let me show you how easy it is. Here, I’m just going to keep it simple with just a signal generator and a multimeter. I’ll set the signal generator to a default 1kHz tone, as I use that a lot. And I’ll set the multimeter to read my reference microphone.
Now I just save this as a .vic file which is a Virtual Instrument configuration file and give it a name – I can do this from any of the virtual instruments that I have open.
Now it’s saved, I can set SoundCheck to “Automatically Load VI Config” in the Launch tab of the preferences menu and set it to the file I just created. Now each time we launch SoundCheck it will load our VI configuration at startup. I just showed you a basic setup, but you can truly customize it for your needs, for example with multiple signal generators pre-set to frequencies that you use a lot, or with multiple distortion meters, each measuring a different distortion type.
You can even save multiple startup configurations with different names – this is great if you have to share your SoundCheck system with colleagues, or have different virtual instrument needs depending on what you are working on.
100 Things #64: Using Statistics to Create Test Limits
The statistics feature in SoundCheck adds the ability to perform a variety of statistical measurements. SoundCheck’s statistics step can work with data, results, or both. Statistics allows users to take a set of data, like frequency responses of multiple devices, and automatically calculate the best or worst fit to average, maximum, minimum, and more. This statistics functionality is not just confined to a sequence, since all the same functionality is available with offline statistics. This is a great solution of performing statistics independent of a sequence, for applications like finding golden units in production testing.
Using Statistics to Create Test Limits
Learn more about statistics and limits in SoundCheck
If you want to learn more about using statistics in SoundCheck, our four-part tutorial series on using statistics with SoundCheck is available to watch here. This series goes in-depth with statistics data, results, processing capability, and offline capability.
Our three-part tutorial series on limits in SoundCheck is available to watch here. This three part series covers the basics of limits functionality in SoundCheck, data, and advanced limit creation.
Video Script:
One question I often hear from customers is “I wrote a sequence to measure my devices. I have the frequency response, THD, sensitivity, but how do I know if this is good or bad?” We have statistics tools inside SoundCheck that can make this determination a lot easier.
It’s important to remember that measurement targets are completely different depending on the device. For example, the acceptable level of distortion in a high end pair of bluetooth headphones, would be completely different than a cheap USB headset made for online meetings. A great place to start is picking out five units that are subjectively “good” devices. We can measure these units in SoundCheck, use statistics to help us generate limits, then compare other devices to this.
Let’s look at a standard headphone test sequence. Right now it’s configured to just run one test, but by adding in a statistics step to the end of the sequence, I can run this test as many times as I like and average all of those different units.
The statistics step has many different features, but let’s look at Mean and Standard deviation. Mean takes the average point of the selected curve or value for every run. If I measure 5 devices and get their frequency responses, the mean is a running average of all 5 devices combined. We can use our mean as a reference curve, and compare each device to this.
Standard deviation outputs plus minus sigma curves, which we define in the editor. For example if I want to make sure that all my devices fall within 3 sigma of my 5 reference devices, I set up my statistics step to output +/- 3 sigma, and after I run my 5 different units these upper and lower sigma curves are added to memory. I can then use these as the upper and lower limits in my test sequence, and pass a device if it falls within this range and fail it if it’s outside the range.
And one final note… If you already captured measurements but didn’t run statistics on it while the sequence was running, all of these same features are available in the offline statistics editor. Just open up your curves from your good units in the memory list and you can run statistics directly through the offline menu.
With offline statistics, you can calculate the Best Fit to Average and Worst Fit to Average curves by finding which unit comes closest to, or furthest away from the average curve. Best Fit to Average can be used to find a reference or “Golden Unit”. This can be used as a sanity check when things go wrong on the production line and for developing limit curves. Some manufacturers prefer this approach because the factory environment e.g. temperature and humidity can vary from day to day and affect devices’ measurement performance.
By measuring the golden unit before measuring newly manufactured devices, the limits can be updated relative to the golden unit under current conditions. Worst Fit to Average can be used to find outliers or bad units that you don’t want to use in your statistical calculations when developing limits. Once you find a Worst Fit to Average curve, simply unselect it and re-run your statistics on the remaining good units.
Do you use statistics to set pass/fail criteria? Let us know in the comments below.
100 Things #63: Measure Frequency and Distortion in Real Time
SoundCheck features a full suite of versatile powerful virtual instruments, including a dedicated frequency counter and distortion analyzer. The frequency counter is perfect for finding the dominant frequency in a signal path. The distortion analyzer includes many different distortion measurement options, and even allows the user to select which specific harmonics to analyze. As with all virtual instruments in SoundCheck, both instruments can be used within a sequence with a virtual instrument acquisition step. Both instruments also include a strip chart recorder, perfect for measuring DUT performance over a long period of time.
Measure Frequency and Distortion in Real Time
Learn more about the frequency counter and distortion analyzer virtual instruments
Read all about SoundCheck’s full virtual instrument suite including the distortion analyzer and frequency counter, plus all of the powerful and useful functionality.
Video Script:
You may already know that SoundCheck includes virtual instruments for quick, on-the-fly measurements. But, did you know SoundCheck has both a Frequency Counter and a Distortion Analyzer virtual instrument?
The frequency counter determines the dominant frequency in a signal path, analyzing it in real time and displaying the primary frequency. This tool is useful for calibrating audiometers, or any device where a pure tone needs to be identified to a very high precision and accuracy.
The distortion analyzer continuously measures the distortion in a signal path. This virtual instrument offers many different distortion measurements, including individual harmonics, total harmonic distortion or THD, where you can select which harmonics to analyze just like in the Analysis step, THD+N, THD and THD+N residual level, and signal-to-noise distortion ratio, or SINAD. In fact, many of SoundCheck’s distortion measurement methods are available right here in the distortion analyzer. There are many different use cases for this analyzer, but one example might be to measure real time distortion characteristics. An example might be to increase the signal level to a DUT using the signal generator, and use the distortion analyzer to see at what level the distortion crosses a particular threshold, for example: 3% THD.
Both instruments allow for linear or continuous averaging and variable time weighting, and limits can be set with clear visual feedback. As with all our virtual instruments, values can be saved to the memory list to be recalled in following sequence steps. This enables you, for example, to trigger a measurement at a certain frequency determined by the frequency counter. And, just like all virtual instruments in SoundCheck, both the distortion analyzer and frequency counter can be used within a sequence using a virtual instruments step.
These tools’ capabilities can be further extended with the strip chart recorder. This addition enables changes in frequency and distortion characteristics to be easily tracked over extended testing periods. For example, using the strip chart recorder with the distortion analyzer allows any changes in distortion percentage to be monitored over hours or even days. Similarly, the frequency counter can be used with the strip chart recorder to test the stability of a Bluetooth device over a time period to identify any problems with jitter or signal dropouts.
What virtual instrument would you like to see in SoundCheck? Let us know in the comments below. For more information on all things SoundCheck, be sure to head to Listen Inc . com.
100 Things #62: Make Directional Measurements with Polar Plots in SoundCheck
SoundCheck’s Polar Plots make directional measurements simple. No matter what device you are testing, whether it be a VR headset, spatial audio, or headset sound leakage, SoundCheck can automate the measurement and turntable control. This means long high resolution measurements become as simple as starting a sequence! We even have a free, prewritten directional measurement test sequence using the new Portland Tool & Die MDT-4000 turntable, available here.
Make Directional Measurements with Polar Plots in SoundCheck
Try our loudspeaker polar plot measurement sequence for yourself!
Our polar plot sequence measuring a loudspeaker is pre-written and ready to use. This sequence measures the polar response of a loudspeaker in both the vertical and horizontal dimensions and displays the measurements on polar plots. This sequence is designed to work with the Portland Tool & Die MDT-4000 turntable.
Video Script:
Making directional measurements in SoundCheck is simple! SoundCheck supports turntables from a variety of manufacturers including Outline, Linear X, B&K and of course, Portland Tool and Die. These can all be controlled through a custom step in SoundCheck to be operated as part of an automated test sequence. Let’s take a look.
Here I have a Portland Tool and Die MDT-4000 turntable – this a great turntable, by the way. I’m going to use this to rotate a speaker, and I have a stationary measurement microphone to capture the recorded waveform. And of course I have SoundCheck on my laptop, along with an AmpConnect 621 Audio interface.
Here’s a simple loudspeaker test sequence that plays a test signal through a loudspeaker and measures the response. Now let’s say I want to measure the response of the speaker every 10 degrees for a full 360 degree rotation. I just need to open up the test sequence….And I am going to add a custom step telling it to rotate the speaker by 10 degrees and re-measure, saving the results in the memory list and plotting them on a polar chart, now I’m going to loop that whole measurement procedure so we continue moving it and measuring until we do a full rotation. And now I’ll edit the display step to get the results output to a polar plot. Now let’s run the sequence…and there you are – fully automated directional measurements!
There are many ways to use this functionality, for example directional measurements on smart devices with microphone and speaker arrays. You can also put headphones or VR headsets on a rotating head and torso simulator and measure the sound leakage that occurs when the noise inside the headphones leaks outside to the point where it’s audible to others around. There are also many applications in spatial audio measurements.
If you want a quick way of getting started with directional measurements, head on over to our website where you can download basic directional measurement sequences for speakers and microphones for a variety of different turntables.
