100 Things #94: Road Noise and Active Road Noise Cancellation Measurements

Road Noise and Active Road Noise Cancellation Measurements are easy with SoundCheck. Everyone’s familiar with measuring headphone active noise cancellation with SoundCheck, but did you know it’s also great for in-car measurements of road noise and evaluation of road noise cancellation systems? Simply connect the USB-powered AudioConnect 2 to your microphones and laptop, and start making measurements. Watch this short video to see how easy it is with this compact and cost-effective package.

Make Road Noise and Active Road Noise Cancellation Measurements

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Read more about in-car road noise measurements.

Learn more about automotive testing using SoundCheck.


Video Script: Road Noise and Active Road Noise Cancellation Measurements

Everyone’s familiar with measuring headphone active noise cancellation with SoundCheck, but did you know it’s also great for measuring active road noise cancellation and road noise reduction in cars?

In this application, you want to measure the road noise at the location of the driver or passenger ears. A simple and cost-effective way to do this is to position two microphones near the outside of your ears or use a Head and Torso simulator. Here, we attached two SCM microphones to a Listen hat using some clips – we call this a low-budget HATS. This has the added advantage that if you are out on real roads, you can measure in the driver’s position.

Our configuration is simple. The microphones are connected to an AudioConnect 2 audio interface for microphone power and signal conditioning. This is a great application for this interface, as it’s USB powered, so you don’t need a power outlet in your car – you can just run it off your laptop. The AudioConnect 2 is connected via a single USB cable to the computer that is running SoundCheck for analysis.

As you can see, it’s a compact setup that easily fits on your dashboard or passenger seat.

To measure road noise, we simply need to drive at a fixed speed, remain silent – that means no talking, coughing, or children in the back seat –  and record for a fixed period of time. You can then look at both the sound pressure level and the frequency spectra of the road noise.

To evaluate a road noise reduction system, simply repeat the measurement with the noise cancellation turned on and subtract one result from the other to provide a value for the noise-reduction system of the car.

This is just one of many automotive audio measurements you can make with SoundCheck. Others include end of line QC, evaluation of components, tuning, Max SPL, impulsive distortion, Buzz, Squeak and rattle, POLQA analysis of communications systems and more. Check out the automotive section of our website for more information.



100 Things #77: Using Confidence Limits for Sequence Speed and Accuracy

SoundCheck’s Measurement Confidence is a powerful way to qualify factors that may influence measurements, like noise, settling time, latency, and quantization. Using the confidence limits feature in the analysis step, SoundCheck can display measurements along with any measured discrepancies. A sequence’s stimulus can be edited with tons of flexible options, including increasing both cycle count and minimum duration of a Stweep’s steps. Adjusting these stimulus parameters can fine tune your sequence, yielding high measurement confidence.

Using Confidence Limits for Sequence Speed and Accuracy

Learn more about using confidence limits in SoundCheck

Our Working From Home with SoundCheck video series features an even more in-depth demonstration of confidence limits, diving into the trade off between measurement speed and accuracy.

Video Script:

There are many factors that affect measurement accuracy. Noise, settling time, latency, quantization, sampling and other impediments, all affect the quality of your measurements.  SoundCheck’s powerful ‘Measurement Confidence’ tool helps you assess how these factors impact your measurements and helps you fine-tune any trade-offs between speed and accuracy. This feature is found in the HarmonicTrak analysis editor on the Distortion tab.

Let’s focus on noise as the source of our measurement error. SoundCheck’s HarmonicTrak algorithm uses FFT analysis to measure the levels for each step of a stepped sine sweep. The shorter the duration of a step, the larger the width of the FFT filter around its center frequency which allows a greater amount of noise to collect in the filter band.  Noise adds to the sinewave and if you measure it 10 times, you’ll get 10 slightly different results. The standard deviation of the 10 measurements is called the standard error which is directly proportional to the noise collected in the FFT filter and to the duration of the step. By evaluating the level of the noise present in the FFT, SoundCheck is able to give you the standard error at each frequency.

Additionally, SoundCheck can produce limits within which you can expect the true value to lie. These are called Confidence Limits and there’s even a sequence included in your Soundcheck installation which demonstrates this feature. Let’s take a look.

The sequence uses three different Stweep configurations to show how the Confidence feature works. SoundCheck’s stimulus editor gives us precise control over the duration and number of cycles per step in our Stweep. In this example sequence, the first stimulus is configured so that each step contains 3 cycles. In the second stimulus, each step contains 10 cycles and in the third stimulus we add a minimum duration value of 10 ms in addition to the 10 cycle requirement. Let’s run the sequence and take a look at the results.

In sweep 1, the confidence limits are quite wide and drop off dramatically at the low frequency and high frequency where the signal to noise decreases due to the lower levels. It’s no surprise, considering the small number of cycles per step. Increasing the minimum number of cycles to 10 dramatically improves the results.  Confidence is overall very good with the exception of the very high frequencies.  In the last sweep, by introducing a minimum duration requirement of 10ms, we can see a further improvement at high frequencies since we are extending the duration of the steps at the highest frequencies.

I hope that this demo gives you a taste of what you can do with the Measurement Confidence feature in SoundCheck.  There’s a more extensive demo of this feature in our Working From Home with Soundcheck video series and further details in the SoundCheck user manual.

Learn more about SoundCheck features and functionality.

Headphone Measurements Demonstrations

In this short video, Steve Temme demonstrates two different headphone measurements with SoundCheck.

In the first demo, he measures a pair of Bluetooth earbuds in an open loop test to obtain frequency response, left/right tracking, THD and sensitivity. He also measures frequency response and sensitivity for the built-in microphone. In the second demonstration, he measures both active and passive noise cancellation of a pair of over the ear headphones with pink noise and speech.

These measurements are made with SoundCheck, the AudioConnect audio interface and the PQC-4149 Bluetooth interface. The SoundCheck test sequences to run these tests are available free of charge on our website.

Headphone measurements demonstrated include:

  • Headphone frequency response
  • Headphone left/right tracking (L/R tracking)
  • Total Harmonic Distortion (THD)
  • Sensitivity
  • Microphone frequency response
  • Microphone sensitivity
  • Active noise cancellation with pink noise and speech
  • Passive noise cancellation with pink noise and speech
  • Total noise cancellation with pink noise and speech

Presenter: Steve Temme
Duration: 10 Mins

Headphone Measurement Resources

Learn more about our headphone complete test sequence (available in the sequences folder of your SoundCheck installation).

Try our ANC Headphone measurement test sequence

Check out our main pages on Headphone Testing, Bluetooth Headphone Testing and ANC Headphone measurements, which includes links to test sequences, relevant products and more.