Audiophiles know their sound production equipment. Technological advancements in headphones, audio recorders and media players command attention in a never-ending search for their next ear altering experience. To help audiophiles in their quest, manufacturers have responded with subsonic and ultrasonic performance offerings that belie current auditory conventions.
“There are many companies making marketing claims that their headphones perform past the range of human hearing up into the ultrasonic frequencies, and we wondered if anybody’s checking these claims,” explains Lenny Hantz, Quality Assurance Analyst at UL’s Audio Lab in Fremont, Calif.
It turns out there wasn’t a recognized standard of HD audio quality, only reviews provided by independent commentators, magazines and websites/blogs. To bridge the verification gap, UL’s Audio Lab developed a program to verify the performance of HD devices, investing in specialized equipment to develop nine core tests—frequency response; phase and polarity; signal to noise ratio; total harmonic distortion plus noise; level; crosstalk; driver matching; playback analysis and recording analysis.
“We have a special head and torso simulator that will test up to 50 kilohertz,” according to Hantz. Plus, “an audio precision analyzer to produce, analyze and test for the frequencies claimed in HD audio products.”
The UL Audio Lab offers both quantitative and qualitative testing of HD and high-resolution audio equipment. Audio devices must pass at least one of the following to qualify for the HD Audio Verified Mark:
- The device must be able to create/record digital files of at least 88.2 kHz sample rate and 24-bit
- The device must be able to play digital files of at least 88.2 kHz sample rate and 24-bit
- The device must be able to produce at least 40 kHz in analog frequency response
- The device must be able to capture at least 40 kHz in analog frequency recording
Subjective testing, which is separate from the Verification Protocol, is also available and includes public listening panel testing to provide feedback on the audio quality of the device. “Participants come into the lab and listen to the device, whether it’s headphones or a media player, and give feedback on they feel it sounds,” explains Hantz.
Participants listen to 10 audio files and provide opinions on the playback quality of each file through the device as well as a final overall score for the audio quality of the device. Additionally, award-winning audio engineers and producers from the San Francisco Bay Area also provide specific feedback on audio characteristics and sound quality aspects through the Audio Lab's expert panel testing.
Once the marketing claim has been qualified, manufacturers can include the UL Verified Mark on device packaging and marketing material. The UL Verified Mark features a unique identifier and a description of the marketing claim. The Mark was deliberately designed to be distinct from the UL Certification Mark, with the most prominent element of the Mark being the marketing claim itself.
Additionally, all UL Verified marketing claims are included in the publicly available UL Verify Database, a tool searchable by manufacturer name, product name and unique identifier.
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