Tag Archive for: bluetooth

Bluetooth Headset Test Sequence

The purpose of this sequence is to test a Bluetooth headset using a mixture of analog and digital channels. First, a Multitone stimulus is created with SoundCheck, played back over the Bluetooth headset (at 8 kHz) and recorded by a head and torso simulator’s ear (at 44.1 kHz). Then the same Multitone stimulus is played back through the head and torso’s mouth simulator (at 44.1 kHz) and recorded via the Bluetooth headset (at 8 kHz).

Due to inaccuracies of clock frequency, the Bluetooth device playback sampling rate is often slightly different than it is specified. Therefore, in SoundCheck, the Recorded Time Waveforms are frequency shifted to correct for the inaccurate sampling rate. The exact device playback sampling rate is displayed.


100 Things #25: Bluetooth Capability Can Be Added to Any SoundCheck System

Bluetooth capabilities are becoming more and more common in modern devices. Luckily, you can add Bluetooth testing capability to your existing SoundCheck system quickly, and be ready to test without huge hardware investments or learning brand new software. Les demonstrates the hardware and software options available from Listen with some typical Bluetooth test setups.

Bluetooth Capability Can Be Added to Any SoundCheck System

Learn more about Bluetooth testing capabilities in SoundCheck

Check out our full seminar, all about Bluetooth testing in SoundCheck. Les Quindipan of Listen, Inc. and Kristopher Hett of Portland Tool & Die demonstrate Bluetooth testing with a variety devices, test parameters, and testing considerations.

Video Script:

A recurring theme you will hear in this 100 Things Video Series is SoundCheck’s flexibility with a wide range of audio test applications and broad compatibility with acquisition hardware. This architecture dates back SoundCheck’s release in 1995, and makes SoundCheck very adaptable to expanding your existing system for other test applications.

Let’s look at adding Bluetooth testing to an existing SoundCheck system.

Suppose you are currently using SoundCheck for traditional speaker, headphone or headset mic testing. Then, you develop a Bluetooth product. It’s very easy to add Bluetooth testing to your SoundCheck system.

Let’s look at these traditional and BT setups side-by-side.

Here’s a traditional wired speaker test diagram next to a wireless Bluetooth speaker test. Note, the tests are nearly identical, but we simply add a USB connected Bluetooth interface which wireless transmits the test stimulus to the speaker under test.

A Bluetooth headphone/headset test is similar to a speaker test, except the stimulus is transmitted wirelessly to two channels- the L/R sides of the headphone, and the response is acquired through the ear simulators.

We can also test the BT headset mic. In this case, the test stimulus is transmitted to a calibrated mouth simulator, and the response is acquired wireless from the headset microphone for analysis.

We offer two different Bluetooth interfaces. The BTC 4149 here is a fully featured interface designed for R&D use. It can test  both sink, e.g. headphones and source devices, e.g. smartphones, with full control over Bluetooth protocol settings, such as explicit control over codec choice and transmitter power, as well as various pairing options. We also have a lower cost option, the BQC 4149, for production applications. This one tests Bluetooth Sink devices only, and offers only the standard aptX, CVSD and mSBC, along with more limited control of Bluetooth parameters. Both these devices use the same chip set, so tests can be seamlessly transferred from one device to the other as they move from engineering to production

The advantage of SoundCheck’s modular architecture is that:

1) Adding wireless Bluetooth testing is an incremental upgrade to your existing SoundCheck system. In other words, you don’t have to invest in an entirely new hardware and software to add Bluetooth testing.

2) Testing wireless Bluetooth remains in a SoundCheck environment, which you are already familiar with.

3) If you are scaling for production, you can spec a lower cost BQC-4149 interface for your production systems.

Bluetooth Testing Seminar

Les Quindipan of Listen, Inc. and Kristopher Hett of Portland Tool & Die demonstrate Bluetooth testing with a variety devices, test parameters, and testing considerations. Kris Hett introduces the Portland Tool & Die Bluetooth interfaces that are used to connect the device under test to the measurement system. He discusses the technical specifications, and explains the differences between these and other types of Bluetooth interfaces. Les Quindipan then demonstrates how these have been fully integrated into SoundCheck for simple plug and play operation, and how they can be used in test sequences. He also highlights some of the algorithms included in SoundCheck that overcome Bluetooth-induced time delays, thus enabling these devices to be tested in a similar way to their wired counterparts. A complete test on a Bluetooth speaker and a Bluetooth Headset is demonstrated.

Seminar demonstrations include:

  • Overview of Portland Tool & Die Bluetooth interfaces features and functionality
  • Portland Tool & Die software control integration with SoundCheck
  • SoundCheck configuration and calibration for testing Bluetooth devices
  • Software control of Portland Tool & Die devices within a SoundCheck sequence
  • Demonstrations of sequence measuring Bluetooth headsets and speakers

Presenters: Les Quindipan, Kristopher Hett
Duration: 30 Mins

Bluetooth testing Resources

  • Our sequence library contains many ready-to-run sequences for testing Bluetooth devices, available for download for no charge.

More about testing Bluetooth devices

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

Updated Bluetooth Interface Supports High Definition and Low Latency Bluetooth

The updated BTC-4149 Bluetooth measurement interface now supports the aptX HD and aptX-Low Latency Bluetooth protocols for accurate measurement of high definition and low latency Bluetooth devices, in addition to the standard aptX, CVSD and mSBC codecs previously available. This enables manufacturers of Bluetooth audio devices to accurately test the audio of the latest high performance Bluetooth sink and Bluetooth source devices, making the same measurements as on traditional audio devices. In addition, the device has a new, larger color screen for improved ease of operation.


The BTC-4149 is designed as a R&D interface, testing both sink and source devices with full control over Bluetooth protocol settings, including explicit control over codec choice and transmitter power, as well as various pairing options.


Also available is a lower cost production tool, the BQC-4149. This tests Bluetooth Sink devices only, and offers only the standard aptX, CVSD and mSBC, along with more limited control of Bluetooth parameters. This model has been updated to use the same chipset as the BTC-4149 to ensure accurate production line replication of R&D tests for those customers who use both interfaces.


Both interfaces integrate seamlessly with SoundCheck, so that all parameters can be set and modified from within a test sequence for fully-automated testing of Bluetooth devices. This accelerates testing, particularly on the production line as it avoids the need to manually adjust Bluetooth settings, reducing the possibility of error. It also enables a device to be tested using multiple Bluetooth protocols and settings by taking sequential measurements using different settings in one continuous test.

Product Information

Practical Measurement of Bluetooth and Lightning Headphones

Picture of Bluetooth Headphone Testing Article reprint

Bluetooth Headphone Testing Article

Author: Daniel Knighten.  Reprinted from the July 2017 issue of Voice Coil.

In this article, Dan Knighten discusses Bluetooth headphone testing and Lightning headphone testing, specifically how to overcome the challenges of measuring headphones with wireless and digital interfaces such as Bluetooth, Lightning and USB-C to make the same measurements as on conventional wired headphones.

Full Article




Article Text

Practical Measurement of Bluetooth and Lightning Headphones

For decades, headphones have been passive devices with a direct, analog interface. Today, we are seeing a proliferation of headphones with wireless Bluetooth interfaces and various kinds of new and often proprietary digital interfaces. These new interfaces include Apple’s Lightning port and USB-C. In all cases these headphones present unique challenges to measurement because they cannot be directly connected to traditional test and measurement systems. In this article, we will explore how to overcome these interface challenges in order to make standard measurements on devices with nonstandard audio interfaces.

Closed Loop and Open Loop Testing
To begin, let’s define what we mean by open and closed loop testing. The test configuration for conventional headphone measurements, as seen in Figure 1, is what we term a “closed loop measurement.” This traditional type of audio measurement has been done for years with
all types of transducers (e.g., loudspeakers, headphones, microphones, etc.), and audio measurement systems can make these measurements without problems. The test signal passes from the audio interface through the speaker/headphone where it is converted to sound
pressure. Then, it goes through the microphone where it is converted back to voltage for analysis. The entire path from input to output is on the same interface, usually in the same domain (analog), and most critically, the analysis system’s input and output sample rate are
perfectly synchronous. The entire measurement from signal generation to capture of the device response simultaneously occurs with just a small amount of input to output delay added by the speed of sound.

In headphones with Bluetooth, Lightning, or other unconventional digital audio interfaces, this loop is broken. The input and output are on two different physical devices, which do not share a sample clock, and the signal goes through one or more analog to digital conversion stages. The delay from input to output of the device is likely quite long, compared to classic analog headphones. In fact, the delay might effectively be infinite. In the case of Lightning-connected headphones, there is currently no third-party solution available for injecting a test stimulus into a Lightning port. In Bluetooth systems, the connection is intrinsically non-synchronous. Bluetooth does not provide a synchronous sample clock across the wireless connection and instead relies on asynchronous sample rate conversion and various other techniques to maintain a glitch-free audio stream. This is what we mean by “open loop.” A closed loop system has a closed loop, synchronous signal chain.

An open loop system does not have a continuous or synchronous signal chain. However, SoundCheck makes it possible to measure all conventional parameters of a device, even when those devices are open loop devices, with a variety of tools including:
• Triggered acquisition—support for capturing measurements on playback devices
• File analysis—the ability to analyze signals captured by recording devices
• Resampling—conventional asynchronous sample rate conversion
• Frequency shift—the capability to align signals between non-synchronous systems

Let’s explore how these tools are applied in some typical test scenarios.

Bluetooth Testing
Figure 2 shows a typical Bluetooth setup. Since we are testing the Bluetooth headset using a Bluetooth interface, it is nominally a closed loop scenario. The audio signal comes out of the analog interface and is transmitted via the Bluetooth interface to the headset. It is then played
by the headset and picked up by the ear couplers where it is returned to the analog interface and computer for analysis. However, what makes this an open loop test is that Bluetooth does not transmit a sample clock and, therefore, the receiver and transmitter are asynchronous.

In this case, we will use frequency shift to align or synchronize the stimulus and response waveforms. Frequency shift uses a stationary reference tone to precisely find the difference in sample rate between two waveforms. Once the exact difference in sample rate is found, one waveform is then resampled with reference to the other. Frequency shift enables precise, conventional measurements to be made on Bluetooth devices despite their asynchronous nature.

When compared to a conventional test, only two changes need to be made. First, a short, stationary tone is pre-pended to the stimulus signal (see the Sidebar article). Typically 1 kHz for as little as 250 ms, this signal provides the frequency reference that the frequency shift step needs to align the stimulus and response signals in an asynchronous test scenario. Second, a
post-processing, frequency shift step is inserted into the test sequence between the acquisition and analysis step.

The rest of the sequence is identical to a conventional headphone test sequence and all normal parameters including frequency response, THD, polarity, rub and buzz, and so forth can be measured.

Lightning Headphone Testing
Any device that does not provide an analog or digital input and output is intrinsically an “open loop” device from a test perspective. Headphones that use the Apple Lightning port for connection are considered open loop because Apple does not provide Lightning audio
output adapters. The only device that can currently play audio into a Lightning headset is an iPhone. Measuring Lightning headphones requires an iPhone or similar Apple device to be used to store and play back the test signal (see Figure 3). This creates several open loop testing
challenges. To test a Lightning connected headphone, we will use three specific tools: triggered acquisition, resampling, and frequency shift.

Again, our test sequence will use a short 1 kHz tone, pre-pended to the normal test stimulus but this time it serves two purposes. First, it triggers a record-only acquisition, so that the test is automatically triggered when playback of the test signal begins. It is also used as the reference tone for frequency shift. Also, if our playback device, the iPhone, is using a different sample rate to the audio interface, we may need to use a resampling step. Finally, frequency shift will again be used to synchronize the stimulus and response waveforms. After the response waveform is captured via a triggered acquisition step and has been resampled and frequency corrected, calculation of the desired measurement parameters can proceed as with any conventional headphone.

Pre-written test sequences for both Bluetooth and Lightning headphones are available at no charge from Listen’s website, www.listeninc.com.

Lightning Headphone Microphone Measurements
Since most headphones now also include a microphone, it is worth mentioning how the microphone on a Lightning- connected headset is tested. The test sequence and method
for this is a little more complex, although ultimately it is really just the converse of testing the earphones. Figure 4 shows a typical test configuration. The preparation of the test signal and the use of resampling and frequency shift steps are identical to testing the earphones of a Lightning connected headset.

The difference is that instead of playing back the stimulus through the earphones and using a triggered, record-only acquisition, the stimulus is instead generated using a calibrated speaker or mouth simulator and recorded on an iPhone. The recorded signal is then transferred back
to the computer hosting SoundCheck and analyzed using a recall step to import the waveform into memory from storage on the iPhone.

Bluetooth and Lightning interfaces add an additional level of complexity to testing that is not there with their analog counterparts. However, because the SoundCheck test system is completely agnostic about where the stimulus and the response waveform are generated and
captured, these tests can be carried out with relatively simple modifications to existing test sequences. In fact, it pretty much comes down to a simple modification to the stimulus signal and some additional post-processing steps prior to analysis—all of which are easily automated.
This enables easy characterization and measurement of Bluetooth, Lightning, USB-C, and future devices with advanced digital audio interfaces.


Preparation of the Stimulus Signal (sidebar)
In SoundCheck’s frequency-shift algorithm, a Fast Fourier Transform (FFT) is used to extremely accurately calculate the centroid of a stationary tone. The result of this calculation can then be used to align or synchronize two signals even if they are sampled at different rates. A short, stationary signal is necessary for the frequency shift algorithm to lock on to. This is easily achieved by pre-pending a 1 kHz, 250 ms sine wave to the stimulus signal. Since SoundCheck enables the creation of compound stimuli, this short, single-tone burst can be followed with absolutely any test signal (e.g., a Farina log sweep, noise, speech, or other non-sinusoidal
The short sine wave also serves as the trigger tone for triggered record, as is necessary for testing Lightning headphones. The trigger tone clearly identifies the start of the signal. Care must be taken to set an appropriate trigger level. If it is too low, ambient noise can cause false
triggering; too high and it will never trigger. The trigger level should be set so that it is above the ambient noise and below DUT output level. The Multimeter virtual instrument is an ideal tool for finding the optimal trigger threshold.

A typical stimulus signal for open loop headphone test is shown in Figure 1. This compound stimulus works for both Bluetooth headphones where the sine wave is used for frequency alignment and for Lightning headphones where it additionally serves as a trigger and reference for frequency shift.


Additional Headphone Test Resources

More about Bluetooth headphone testing

Headphone Testing main page


Bluetooth Headset Testing

Screenshot of final SoundCheck display of Bluetooth Headset Testing Sequence

Final display of Bluetooth Headset Testing Sequence

This Bluetooth Headset testing sequence for SoundCheck measures the send and receive performance of a stereo Bluetooth headset with a built-in microphone using a mixture of analog and digital channels. The left and right earphones are measured simultaneously with a stepped sweep from 20kHz to 20 Hz using two Bluetooth profiles: A2DP and HFP. The mic is measured with a stepped sweep from 8kHz to 100Hz using the HFP profile.

A short 1kHz tone is pre-pended to the test stimulus which serves as a reference tone for resampling and frequency shift operations. Post-processing resampling and frequency shift precisely synchronizes the stimulus and response waveforms prior to analysis. In this case, the HarmonicTrak algorithm is used for frequency and THD analysis. A2DP frequency response and THD curves are displayed on the first display, followed by A2DP & HFP curves superimposed on a subsequent display. Lastly, the Bluetooth headset’s microphone is tested with HFP and its frequency response is shown on the final display along with the previously collected data.


Comparison of Wired and Wireless (Bluetooth) Speaker Response

This test sequence performs frequency response and distortion measurements of a Bluetooth speaker using both a wireless Bluetooth and wired stimuli; then compares the results. This sequence is configured for use with a Portland Tool & Die BTC-4149/4148 or BQC-4149/4148 Bluetooth interface.

Initially, the sequence prompts the operator to turn on the Bluetooth device under test and set it to pairing mode. BTC message steps will connect the Bluetooth device (operator selects the device from a list of detected Bluetooth devices) and connects Bluetooth audio. A 1 kHz test tone is transmitted, and if detected, the test sequence proceeds. A stepped sine sweep from 20 kHz to 100 Hz is played wirelessly to the Bluetooth speaker and measured via a calibrated reference mic.

Two post-processing steps convert the sampling rate and alignment of the response, then an analysis step calculates the frequency response and THD. The Bluetooth is disconnected, and the Bluetooth frequency response and THD curves are displayed on graphs. The operator is then prompted to connect the wired analog input into the Bluetooth speaker, and the same measurements are performed using the analog connection. Analog frequency response and THD curves are temporarily displayed on graphs, followed by graphs containing both Bluetooth and analog curves for comparison.


New Production Line Bluetooth Interface

BQC-4148_smallThe new BQC-4148 Bluetooth interface is designed for high volume production line testing of Bluetooth sink devices such as headsets, speakers and car kits. It offers control over the CODEC choice, sample rate, and transmitter power, enabling devices to be specifically tested under the conditions that they need to operate

The unit is rugged and compact, measuring just 30 x 64 x 136mm. With only one connector – a USB for connection to the computer for power and control – it is simple to use and offers minimal potential for incorrect operation. It can be controlled via the USB virtual com port using a command line utility, or from within SoundCheck using the control utility via a system step for simple integration with your test sequences. Although it is less full-featured than its R&D counterpart, the BTC-4148, it is approximately half the cost.

See full details