Lightning Headphone Test (Open Loop Test)

open_loop_headphone_screenshotThis sequence tests a stereo headphone connected to a portable audio device such as a mobile phone or MP3 player. It is particularly useful for testing headphones with proprietary connectors such as the Lightning connector which otherwise can’t be tested in a conventional “closed loop” test configuration.

The test stimulus is created in SoundCheck, saved as a WAV file and loaded on to the portable device for playback. Both left and right earphones are measured simultaneously using a continuous log sweep from 20 Hz to 20 kHz. The sequence uses a short 1 kHz tone, pre-pended to the normal test stimulus to automatically trigger the test when playback of the test signal begins; it also serves as reference tone for any frequency shift calculations. Post-processing precisely synchronizes the stimulus and response waveforms, and then calculation of the measurement parameters proceeds as with any conventional headphone. In this case, analysis is performed using the Time Selective Response (TSR) algorithm which performs THD and fundamental frequency response analysis simultaneously in addition to producing an impulse response. The fundamentals are then post processed to derive the sensitivity of the left and right channels at 1 kHz.


Listen Awarded Patent for SC Amp Amplifier

patentListen’s revolutionary audio test amplifier, SC Amp, has been awarded US Patent # 9,386,387. This patent covers Listen’s unique high accuracy single channel impedance measurement method, which used a unique feedback circuit to offer dual channel accuracy using just a single channel. This enables full electrical and audio tests to be carried out simultaneously and with high accuracy using just 2 channels.

Specifically designed for the audio test market, SC Amp also incorporates several other features unique to the needs of audio test and measurement, such as low distortion (THD <0.025%) and a low noise floor (>100dB). Fixed gain eliminates calibration errors as there is no gain knob to be accidentally knocked or tweaked when it is in use. It supports the application of a DC voltage offset to the AC signal for testing transducers under adverse conditions, and features overload/output protection to prevent damage in case of shorting or overload.

Many unnecessary features found in regular audio amplifiers have been eliminated to keep production line operation simple and error-proof. Although it is designed to integrate seamlessly with Listen’s SoundCheck audio test and measurement software, it will also work well with other brands of test system.

Listen president, Steve Temme commented, ‘We are thrilled that the innovative design of this product has been recognized with this patent, and we are confident that this method will be quickly recognized by the marketplace.’




New Manufacturing Team

evan_and_nickListen has expanded its manufacturing team with the addition of Evan Driscoll (left in picture) as Production Supervisor.  Evan graduated from Wentworth Institute of Technology in 2015 with a B.S. In Electronics Engineering Technology, where he also received the President’s award. Evan is very familiar with manufacturing at Listen, having held several internships and temporary positions at Listen over the past 3 years.

Evan replaces Nick Alston (right in picture), who has been promoted to the position of Manufacturing Supervisor after 2 years in the Production Supervisor role. Together, Nick and Evan manage all of our manufacturing and hardware assembly, test, and QC, ensuring that products are build and delivered on-time to high manufacturing standards.

A visit to

Headphone Test using SoundCheckAbout, part of the USA Today network, carries out quantitative reviews on a wide range of products including appliances, headphones, cameras, televisions and more. Since the beginning, their reviews have been built on the principle of using standardized scientific testing procedures to examine the performance of products, and a proprietary scoring method to ensure a level playing field amongst all manufacturers. Recently, I met with senior scientist Julia MacDougall, and received a tour of the facility and some insight into their headphone test methods, as well as a demonstration of their recently upgraded SoundCheck system.

The large brick building in Central Square, Cambridge, is in a part of town renowned for its young start up culture and unconventional work environments, so it’s no surprise to see a ping pong table next to the large, glass-walled conference room. However, once you get beyond the main lobby it is a labyrinth of test labs, each designed for testing a specific product. A room dedicated to camera testing features various test pictures on the walls, as well as 3d models with many moving and rotating parts to evaluate the camera’s capture of movement. Another lab was filled with massive flat screen televisions that were being tested for display performance, color measurement, luminance, contrast and more. Perhaps the most impressive was the appliance lab, where staff get to do their laundry while they work (in the interests of testing the washers), as well as working their way through many loads of white towels and stain strips that are marked with red wine, chocolate, sweat and more to scientifically evaluate the performance of the washing machines. Dishwashers, dryers, microwaves and ovens are also tested here, and a dedicated temperature and humidity controlled room contains many refrigerators filled with ‘dummy food’, the temperature of which is continuously monitored. The floor above the test labs is where their testers retreat to write up product reviews for their website, away from the whirr of tumble driers, swishing of dishwashers and stepped sine waves from the audio test lab.


The Audio Test Lab

The area that interested me the most was the smallest test area – the audio lab. Headphones are small and the test equipment is also compact, so a large room is unnecessary. has been using Listen’s SoundCheck software since they first started looking for an objective way to test audio products back in 2007. Back then SoundCheck was being used for measuring mobile phones – smartphones were in their infancy, the next ‘hot product’, and was the first review website to measure sound quality of a wide range of phones.

Full Story

New SoundCheck Brochure – Chinese

Our new SoundCheck® brochure is now available in Chinese. This short 12 page brochure is a top-level overview of the SoundCheck audio test system and associated hardware.

download_pdf_icon Download Electronic Version

or complete the form below to request a hard copy.

New SoundCheck Brochure

Our new SoundCheck® brochure is now available. This short 12 page brochure is a top-level overview of the SoundCheck audio test system and associated hardware.

download_pdf_icon Download Electronic Version


or complete the form below to request a hard copy.

Open Loop Microphone Testing – Updated for SoundCheck 14

open_loop_mic_test_final_displayThis updated version of our open loop microphone testing sequence is simpler to set up and faster to implement, thanks to a new feature in SoundCheck 14 – the ability to use values from the memory list to trim the waveform before analysis.

In this sequence, two common microphone measurements, frequency response and sensitivity are made on a microphone embedded in a recording device. Since the response of the device cannot be captured simultaneously with the stimulus in these devices, the signal is recorded on the device under test, transferred to the computer running SoundCheck via a recall step, and analyzed.


Al Flint Joins Listen, Inc.

Al_FlintAudio test and measurement specialist, Listen, Inc.  has strengthened its engineering team with the appointment of Al Flint as Engineering Manager.

Al has spent the majority of his professional career in the audio industry, designing award-winning products and managing product development teams. Al’s career began at Sony Professional Products, where his designs included mic preamps and equalizers for the MXP-3000 mixing console. He then spent many years at Lexicon, where his technical contributions can be found in several effects processors. When Lexicon entered the consumer marketplace with digital surround sound processors, Al not only made design contributions to these products, but also established the development team and helped round out the Lexicon product line with multi-channel amplifiers and DVD players. After their acquisition by Harman, Al led a highly skilled team that designed Mark Levinson products, including several critically acclaimed amplifiers. After spending four years in the solar industry, where he managed development of high-power inverters, Al is returning to his audio roots and passion, and is excited about leading the development of cutting-edge audio and electroacoustic test and measurement products at Listen, Inc.

Open Loop Microphone Test

open loop microphone test final displayThis sequence demonstrates the two most common microphone measurements, frequency response and sensitivity, on a microphone embedded in a recording device such as a smartphone or tablet. Typically when measuring a microphone the response of the device can be captured simultaneously with the stimulus. However, with devices such as voice recorders and wireless telephones forming a closed loop can be cumbersome or impossible. This sequence demonstrates how to measure such a device by recording the signal on the device under test, transferring that recording to the computer running SoundCheck and then using a Recall step to import the recorded waveform and then analyze it.

The sequence operates by prompting the operator to begin recording on the device under test and then a stepped sine sweep is generated from 10 kHz to 100 Hz through a source that has previously been calibrated to produce 1 Pascal across the frequency band. The operator is then prompted to transfer the recording to the computer and then to load the file in to SoundCheck via a Recall sequence step. The recorded signal is sample rate converted and frequency shifted to match the stimulus and then analyzed with a HarmonicTrak analysis step, which calculates the response curve. A post processing step is then used to extract the level at 1 kHz, the sensitivity value. Limits are set around both the frequency response and the sensitivity, the default values should be adapted to your particular device.

The final display shows two graphs. The top X-Y graph displays the data at its absolute level in dBFS/Pa (since the imported recording is digital, the results will be in FS or dBFS rather than Volts or dBV). The lower graph shows the same response curve but normalized to 0 dB at 1 kHz. This is a common way of displaying microphone frequency response and applying limits.