Tag Archive for: 100

100 Things #90: Curve Smoothing

Curve smoothing in SoundCheck allows for non-destructive processing of data, resulting in smooth and easy to visually understand curves. Curve smoothing can lessen the effects of reflections in the test space, reduce noise, or make curves less jagged for publishing data. The smoothing post processing step in SoundCheck features an array of different, to facilitate different levels of the smoothing process, including various smoothing widths and windowing options.

Curve Smoothing

Learn more about SoundCheck post processing options

SoundCheck has a full suite of post processing capabilities including curve smoothing, resampling, resolution, curve arithmetic, and more.  Read more details in our SoundCheck features and applications section.

Each sequence uses a stimulus configured to the device under test, and recommended hardware.

Video Script:

Curve smoothing, as its name suggests, is a useful post-processing option that turns your jagged lines into smooth curves. It  may be applied to a curve for a number of reasons – to reduce the appearance of noise in the signal, to minimize reflections and other artifacts from the measurement environment, or simply to make a curve look better for presentation in sales and marketing literature. When smoothing is applied, the points of the curve are modified so that individual points that are higher than the immediately adjacent points are reduced, and points that are lower than the adjacent points are increased.

SoundCheck uses sliding-average smoothing also known as “boxcar” averaging where each point in the curve is replaced by the average of n adjacent points where n is a positive integer known as the smoothing width.  SoundCheck supports standard 1/n octave smoothing widths from one octave to 1/24th octave as well as user defined log and linear values.  In addition to a default rectangular window, a Hanning window may also be applied during the smoothing function. Smoothing is symmetrical at the midpoints of the curve but tapers to zero at the curve’s end-points.  If the curve has uneven or non-standard spacing in the frequency domain, interpolation is used.

In addition to the standard Smoothing post-processing step, the smoothing function is also available in the Resolution post-processing step. This is useful when the final curve resolution is higher than or “not a mathematical factor” of the original resolution.

This feature’s been available in Soundcheck since it was launched in 1995. If you haven’t tried it yet, check it out!

100 Things #89: Apply Equalization To A Test Stimulus

Did you know you can equalize a stimulus in SoundCheck to remove the influence of hardware and components from your measurements? All of SoundCheck’s stimulus options can have EQ applied, include Stweep, waveforms, noise, and more. An EQ can also adjust a stimulus to focus on different frequencies, like boosting low or high frequencies for power testing. THD+N measurements benefit from this ability, as even applying a flat EQ curve to a Stweep smooths out frequency transitions.

Apply Equalization To A Test Stimulus

Learn more about SoundCheck stimulus flexibility

The stimulus is just one part of the completely flexible SoundCheck system. Learn more about SoundCheck’s features and applications.

If you want to try for yourself, our SoundCheck sequence library includes applications from measuring loudspeakers to microphones, VR headsets to cars, and more. Each sequence uses a stimulus configured to the device under test, and recommended hardware.

Video Script:

Did you know you can equalize any stimulus inside SoundCheck during its playback? In any test application, it is important to ensure that the inherent characteristics of the measurement hardware do not influence the measurement. For example, if you’re using a source speaker to measure a DUT microphone, you don’t want the loudspeaker’s frequency response to influence the measurement. You may also want to apply your own custom EQ curve to weight certain frequencies different, for example, boost low frequencies more than higher frequencies for power testing. You can import whatever EQ you prefer.

We can also equalize the source speaker using a reference microphone. First, we measure the speaker’s response, then invert it to give us the EQ curve. This curve can then be applied to any stimulus playing through the source speaker to correct for both magnitude and phase non-linearities.

When you check the ‘Apply EQ’ checkbox in SoundCheck’s stimulus step, the EQ curve is applied to the stimulus and saved to the memory list, ready for playback during the acquisition step.

This feature is available for all stimulus step types. For step-based stimuli such as Stweep and Multitone, where the stimulus doesn’t have all frequency components, EQ is applied only at those frequency points that are present. For Broadband stimuli like speech, music and Noise, ‘Apply EQ’ behaves like a time waveform filter.

There’s also another reason why you might want to use EQ in a step based stimulus such as a Stweep. When EQ is applied, even if there is no EQ curve, the transition from frequency step to frequency step is smoothed. This is particularly helpful for measurements such as THD+N, which are sensitive to ringing.

Naturally, ‘Apply EQ’ can be turned off if you want to characterize the speaker itself.

SoundCheck’s stimulus step provides many advanced options for a wide range of use cases. To learn more, check out our website or speak to your local sales engineer.

100 Things #88: SoundCheck Support Audio Over IP

SoundCheck supports testing audio over IP using Dante. Dante allows a connection between testing computers and devices over long distances, up to 100 meters. Audio over IP also supports large channel counts, which is perfect for multichannel testing across multiple rooms in a facility. SoundCheck flexible hardware compatibility means networked audio devices can be configured just like any other audio interfaces. In an R&D lab, multiple test labs can have data transmitted to a central SoundCheck system.

SoundCheck Support Audio Over IP

Learn more about Listen audio interfaces

Read on for more information and technical specifications of the AmpConnect 621AudioConnect 2. Audio interfaces can be used with a variety of test hardware including Bluetooth interfaces, turntables, accelerometers, and more. Check out all of SoundCheck’s compatibility with audio testing hardware.

Video Script:

SoundCheck is known for its flexibility to work with any soundcard or audio interface, but did you know it also supports Audio over IP using Dante?

Dante by Audinate allows audio to be transmitted over a standard local IP network. This offers simplified connections where your audio interface is located a long way from your SoundCheck computer, for example if it’s in a test lab or anechoic chamber. Connecting via a Dante interface and CAT 5E or 6 ethernet cable allows data to be transmitted up to 100 meters or more using your existing ethernet infrastructure – something that would be impractical and expensive with standard audio cables. It also offers high channel counts, and the network can be expanded with a high-speed network switch. 

The Dante Interface, for example the RME Digiface Dante,  is connected to the SoundCheck computer via USB and it routes the audio to and from any Dante device connected to the network, such as this Lynx Aurora. It also tracks latency over the Dante network. SoundCheck’s hardware editor displays all devices routed through the Dante Controller as Dante Channels in the SoundCheck Hardware Editor, where they can be treated exactly the same as any other input or output channels to enable a full range of audio tests.

Let’s take a look at how this might work for a speaker test. The Dante equipped Aurora interface is our test hardware, providing the output signal to the speaker, the microphone power, and receiving the signal from the microphone. It’s connected to the network via its ethernet connection.  At the other end, the networked Dante interface is connected to the USB port of the SoundCheck computer where it acts as a hub for any Dante-equipped devices – in this case the Aurora. These devices then appear as a single ASIO audio interface with a USB 3 connection to the SoundCheck computer. From this point, you can configure your audio test exactly the same way as usual, and the Dante controller will handle the signal routing and synchronization of all Dante devices, even if they are different.

Multiple Dante Audio Interfaces can be connected to increase channel count. This setup, for example,  allows for 32 balanced line inputs and outputs through the Lynx Aurora(n) with an additional 12 balanced microphone inputs with phantom power through the RME 12Mic-D. 

Audio over IP has many applications in both R&D and production environments. In the R&D lab, it’s a simple and cost effective way of transmitting data from a remote test lab to a central computer, or to enable a fully mobile audio setup that can be moved around the facility. In production applications it enables centralized data collection from many different production lines. Contact your sales engineer to learn more.

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 #86: Listen’s Latest Generation Audio Interfaces

Traditional sound cards have drawbacks for audio testing, such as physical controls that can easily be altered, cabling errors, and the need for manual calibration. Two interfaces in our next generation of audio testing hardware: AudioConnect 2, and AmpConnect 621, fix these common problems. Both interfaces feature high resolution audio inputs and outputs, TEDS compatibility, microphone power, and internal signal routing. AmpConnect 621 features a built in amplifier and impedance measurement. AudioConnect 2 is portable and can be fully powered over USB type C.

Listen’s Latest Generation Audio Interfaces

Learn more about Listen audio interfaces

Read on for more information and technical specifications of the AmpConnect 621, AudioConnect 2. Audio interfaces can be used with a variety of test hardware including Bluetooth interfaces, turntables, accelerometers, and more. Check out all of SoundCheck’s compatibility with audio testing hardware.

Video Script:

Since SoundCheck was launched in 1995, it has become a standard as an affordable and flexible audio test and measurement system using pro audio soundcards as an audio interface .  But did you know that we also offer our own audio interfaces?

You may wonder why, since soundcards offer so many advantages, so let me share some secrets about why we designed our own hardware, and some of its lesser-known benefits.

When correctly calibrated, high-end soundcards are accurate and cost-effective, especially for high channel counts. But they do have some drawbacks, particularly when used on the production line. Common pain points with sound cards include:

  • Cabling errors – it’s easy to connect something up wrong, or to have a faulty or loose cable 
  • People may accidentally adjust the controls on the soundcard, especially in a busy lab or factory environment – if someone fiddles with your gain control mid way through a production run, you’re going to have a problem!
  • It’s not a big deal when you only have one soundcard to set up, but if you are configuring 30 or 40 production lines, it takes time to configure the channels and calibrate everything. And on top of that, your test integrity depends on this being done correctly.

Our latest generation hardware combines high resolution audio inputs and outputs with TEDS compatibility, microphone power, internal signal routing, and in some cases amplifiers and impedance measurement, to simplify your setup.

These are our two latest audio interfaces, AudioConnect 2 and AmpConnect 621. AudioConnect 2 is our ultra-portable, laptop-powered, low cost 2-channel interface. It has 2 input and 2 output channels and a headphone output. The inputs offer both constant voltage power for our SCMs, and constant current for IEPE microphones and all inputs support TEDS. It’s great for headphone measurements, or for a portable setup. AmpConnect 621 has six powered microphone inputs and two output channels, as well as a built in amplifier and impedance current sensor. This one’s great for multi-channel applications such as measurements with a 6-mic array, or when you need to drive a passive speaker or artificial mouth.

So first off, you can see that these are more than just a soundcard – we’ve put all the functionality you need in one box, with all the signals routed internally, This means that the only connection you have is one USB cable and that makes it hard to mess up your connections. So we can take a speaker testing setup that looks like this and replace it with this. And it actually costs less than all the separate components.

You’ll also notice something missing – buttons. There are no knobs or buttons on the front panel, although we do have level and overload indicators so you can be sure that everything is operating within maximum dynamic range. All control is via the software. This means that once you set your hardware configuration as part of your test sequence, no-one can deviate from that at all – either by adjusting knobs, or by incorrectly setting it up in the first place. This ensures that your test is being run correctly, and it’s particularly useful if you are relying on 3rd party manufacturers to run your tests. If you specify the hardware, software and test sequence, you can guarantee your product is tested to your exact standards with no room for error.

Another benefit of Listen hardware is fast setup with seamless plug and play operation. The calibration data is stored on the device’s firmware so when you connect your interface to SoundCheck, the system reads the calibration values automatically so there’s no need for manual calibration. The input channels also automatically populate with sampling rates, and the device self-test requires no additional cabling as all switching is internal. If you’re using TEDS microphones, you can also automatically read this data too.

So, as you can see, although we always have and always will support a wide range of soundcards, our own hardware offers some clearly defined benefits. Conversely, there are other situations, for example high channel count, where a sound card is the more cost-effective option. Our goal is test system modularity and flexibility, so sound card or audio interface – the choice is yours.

100 Things #85: Integrate Soundcheck Data With Your Database

Using SoundCheck as part of your test setup and database is easy. SoundCheck’s data can be saved directly to Microsoft Access or an SQL database, all from within a sequence. This includes curves, values, results, and waveforms. SoundCheck’s autosave sequence steps can automatically gather, format, and export sequence data. Plus, with TCP/IP integration, SoundCheck’s data can be accessed and ready to use in your own program.

Integrate Soundcheck Data With Your Database

Learn more about SoundCheck integration

SoundCheck includes examples scripts for externally controlling SoundCheck via TCP/IP. C sharp, C++, LabVIEW, MATLAB, and Python examples are included.

Our SoundCheck tutorial series covers everything you need to know to get testing with SoundCheck, including how to configure SoundCheck autosave steps with a database. Check out the Autosave to Database tutorial, or the full tutorial playlist.

The SoundCheck manual gives detailed written instructions on setting up your database with SoundCheck, configuring TCP/IP connections, and more.

Video Script:

SoundCheck performs many measurements on your audio device – frequency response, sensitivity, harmonic distortion, perceptual distortion, transient distortion, directivity, pass/fail results and more. When you test hundreds, or even thousands of devices a day on a production line, that’s a lot of data. Everyone wants to manage this differently, so we offer several different database options for seamless integration with your manufacturing and business intelligence systems.

Directly in a SoundCheck step, you can save your curves, values, results, or waveforms to a database. Using an autosave step you can make a connection to a Microsoft Access or SQL database so that whenever your sequence runs,  the data is sent to the database. Industry standard tools can then be harnessed to run analytics over large data sets. For example, a procedure could be created to examine the frequency response on all measured devices on the database and create limits based on the average. 

Even if you’re not using a database, SoundCheck still has options to get your data into a format that’s easy to work with. In addition to the options shown directly in the autosave editor  – that’s text, csv, Excel, TDMS, Matlab .dat, .wfm, and.res, there’s also a plugin available to transfer data to WATS. WATS is a full test data management platform created by Virinco that can quickly and easily take production data and place it into dashboards to help see your production statistics at a glance. 

If these options aren’t enough, all the data, curves, and other  items saved in SoundCheck’s memory list, can always be accessed directly via TCP/IP. This means you can write your own customized program to collect exactly the SoundCheck data you need. Simply read the memory list items using a TCP/IP connection to the SoundCheck computer and you’ll have all the measurements ready to go in your own program. We have some very basic examples of this included with the Soundcheck installation in the external control examples folder, but the final product can be as specific to your use case as you need. 

Hopefully this brief introduction has demonstrated how SoundCheck’s flexible data management enables it to be easily integrated into your test environment. Check out the SoundCheck manual for detailed information on how to set up database connections, use TCP/IP and more.

100 Things #83: Open Loop Measurements Of Smart Devices

Open loop testing enables measurement of smart devices, phones, and any device that cannot play a stimulus and record at exactly the same time. Both speakers and embedded microphones on these devices can be measured with SoundCheck, thanks to it’s module test architecture. With SoundCheck, the stimulus and acquisition are separated, so a stimulus file can easily be loaded onto a smart device and triggered either manually or via network commands. For internet connect devices like smart homes, stimulus files can be uploaded and played directly from the cloud.

Open Loop Measurements Of Smart Devices

Learn more about testing smart devices

Our full Smart Device Testing seminar features test demonstrations of smart homes, Bluetooth headphones, and active noise cancellation. Device design considerations and individual component tests are shown, and how SoundCheck can measure audio quality from R&D to production.

Video Script:

Open loop testing lets us measure a device when it’s not possible to play the stimulus and record the response from SoundCheck at exactly the same time, for example smart devices, phones and more. This is simple in SoundCheck, since its architecture has always allowed analysis to be performed independently of acquisition. In fact, we pioneered open loop testing, originally for testing MP3 players,  back in 2006 – a good 10 to 15 years before others started implementing this capability.

Let’s start by explaining how open loop testing is different from conventional closed loop tests. In conventional audio tests, such as speaker and microphone tests, the stimulus playback and response recording occur simultaneously. The two signals are correlated, and ready to analyze.

Devices such as mobile phones and smart speakers do not have a simultaneous input/output audio path, but we can test both the speakers and the microphone using open loop testing. In open loop testing, the stimulus includes a trigger to tell SoundCheck when to start recording. 

Let’s look at a mobile phone test. For the speaker, a stimulus file is loaded onto the phone and played back either manually or via a command. SoundCheck records the response using a trigger record acquisition. To test the microphone, a stimulus is played through a mouth simulator, and manually or via a command recorded to the phone. The recording is then transferred to SoundCheck for analysis. 

I’ve already uploaded the stimulus file onto my phone, and I’ll manually playback the stimulus file and trigger the record in SoundCheck.  This short “sine chirp” in the stimulus file serves as the trigger and is not analyzed. This is  a sophisticated level and cross-correlation trigger that is more robust and less susceptible to false triggers than simple level and frequency options. The test sequence then uses resampling and  frequency shift post processing steps in the sequence to correct for sample rate mismatches and slight sample clock differences between the device under test and your test interface. This enables perfect alignment of stimulus and response for accurate analysis. I’ll run the sequence…

There you go. The top graph displays the frequency response of the phone’s speaker, to the right is the recorded response superimposed over the stimulus, the bottom graphs include THD, Rub and Buzz and Enhanced Rub and Buzz.

Let’s look at some other examples. These Apple “lightning” wired  earbuds can’t be tested using a standard headphone test interface as these do not support the proprietary connector. However,  the lightning earbuds can be connected to an iPhone, and the phone can playback the test stimulus.

Open loop testing even allows testing via the cloud. With a smart speaker, the stimulus file can be uploaded to the cloud, and accessed and played back from the cloud via voice command through the speaker, using the same triggered record acquisition that I demonstrated earlier.

These are just a few common examples, but with these methods, you can measure just about any device or system that does not have a direct wired connection between signal input and output. Check out our seminar on smart device testing for more open loop demos.

100 Things #82: Measuring Audio Leakage From A VR Headset

Virtual Reality Headsets may be new to the market, but users already expect excellent sound quality to enhance the immersive experience. SoundCheck’s flexibility means you can measure almost any device including VR headsets, by leveraging it’s step-based sequence functionality. VR headset measurements can be made with the same parameters as any other headset; frequency response, perceptual distortion, phase, and more. With the addition of the MDT-4000 turntable, headset audio leakage can be measured to better quantify what people nearby would hear from a user’s VR headset.

Measuring Audio Leakage From A VR Headset

Try VR headset measurements for yourself

Our pre-written VR Headset Leakage Measurement sequence takes the guesswork out of VR headset measurements, with commands pre-programmed to work with the PT&D MDT-4000 turntable.

Video Script:

Virtual Reality and Augmented reality headset measurements are made in pretty much the same way as other headphone and headset measurements. However, one thing to be aware of is that VR and AR headsets often have the speakers located in the headband. This means that you need to use a head and torso simulator where the speaker can be in a realistic position relative to the ear, rather than lower cost couplers or headphone test jigs that rely on the headphone sitting directly in, or on the fixture to create a tight seal. 

With this setup, you can use any of our standard headphone test sequences to measure frequency response, phase, distortion, impedance, sensitivity and other parameters.

Another measurement that is particularly useful for virtual reality headset characterization is headset leakage. With the speakers unoccluded on the headband – not sealed on the ear canal –  there can be considerable acoustic leakage, and designers try to minimize the noise emanating from the device so as not to annoy other listeners nearby. 

Here, we’ll use a measurement microphone to simulate what the nearby listener hears from the person wearing the VR headset and a turntable to produce a polar plot showing the level of leakage from the VR headset versus angle. You can set the microphone position to whatever distance you want to measure, and define the test level. When we run the sequence, it plays a test signal and the microphone records the acoustic leakage. The turntable then rotates through 10 degrees and re-measures. We repeat this through 180 degrees, and mirror the results to get a full 360 degrees plot. This test sequence also shows the frequency response at each angle. This sequence is available free of charge on our website if you want to try it out.

100 Things #81: Using Statistics to Overcome Fit Variation for Headset Measurements

SoundCheck’s statistics allows for multiple measurements from a sequence to be analyzed together, to determine results like average and standard deviation. Using statistics can overcome placement variations when measuring headsets on a head and torso simulator. This sequence demonstrates a measurement of a USB headset, performed five times, where the headset is removed and repositioned on the HATS each time. SoundCheck’s statistics then take these five measurements, account for the differences in placement, and display an accurate set of measurement results. If you are testing to standards then statistics makes measurement of communications devices fast and repeatable.

Using Statistics to Overcome Fit Variation for Headset Measurements

Try measurement statistics in SoundCheck

Learn more about our pre-written TIA-920-B test sequence mentioned in this video. This pre-written sequence tests to TIA 920-B, a comprehensive US dual-bandwidth standard that applies to both narrowband (NB) and wideband (WB) devices.

Video Script:

Statistics have been a feature in SoundCheck for a very long time. But did you know that statistics can be used to overcome fit variation when measuring body-worn devices? Let’s look at how we can use this feature to make repeatable TIA-920B measurements on headsets?

For realistic and accurate results, headsets and other body-worn devices should be measured on a Head And Torso Simulator, or HATS, placed just as worn by real users. Unfortunately, small changes in position can lead to significant changes in both the level and the sound quality, whether on a real person or HATS.

For example, when placed carefully, the receiver of our USB headset sounds like this. (Audio example 1: proper placement)

When placed poorly, it sounds like this. (Audio example 2: improper placement)

To obtain repeatable results, we make several measurements and average the results, using the Statistics Step.

The headset is completely removed from HATS after each measurement, then repositioned for the next. With practice, 5 measurements are usually enough. This procedure is defined in ITU-T P.380 and IEEE 269 and used in Listen’s pre-written sequences that implement TIA 920-B.

Let’s make some measurements.

We are testing a USB headset that has two receivers and a boom microphone, intended for speech communication. There may be some speech-sensitive signal processing, so the test uses real speech. The signal is played out to the receivers first, then to the HATS mouth.

When the first measurement is finished, the receive frequency responses and single parameters such as output level are shown on the top line

In a similar way, the sidetone frequency responses are on the second line, and the send frequency response is on the bottom line.

After 5 measurements, with re-positioning between each measurement, we can see the individual frequency responses. Let’s take a closer look at the Left receive frequency response. The individual frequency responses are in gray, the current measurement in white, and the current mean in blue.

After the last of the measurements, we can see the mean results. Tolerances from the standard have been applied to the mean receive and mean send frequency responses.

The standard deviations show the repeatability of the individual measurements. If the standard deviations are within the tolerances, the mean results are acceptable. When results from 2 or more operators using this method are compared, the mean results will usually be very close, even if the individual measurements are somewhat different.

Statistics helps overcome fit variation to make accurate and repeatable measurements of headsets, as well as most other body-worn devices such as helmets, goggles, parrots and so on. And, if you are making TIA-920-B measurements on such devices, you can save a lot of test writing time with our pre-written TIA-920-B sequences. These can be used for USB, Bluetooth or wired analog devices, and there are also open-loop sequences for testing devices that connect to a server.