audioXpress Magazine      April 2022

  audioXpress remains the authority on audio and reproduced sound by connecting manufacturers and distributors with developers, buyers and consultants around the globe! It's readers are the audio product designers, consultants, integrators, DIY enthusiasts, opinion leaders and your best customers. All of them agree that the coverage of trending topics, unique in the audio industry, make audioXpress a must read.

Every month, audioXpress combines the best educational articles on topic such audio electronics, speaker and headphone design, amplifiers (from tube to Class D), acoustics, practical test and measurement, audio engineering praxis, and standards. audioXpress provides inside stories on new audio developments, on R&D Stories, the most complete objective reviews of innovative products and software, and selects some of the best DIY audio projects from worldwide experts.

From The Editor's Desk
4 From the Editor's Desk
Directions For Hearables We are starting to have some ideas about this technology.
Editorial By J. Martins

5 Client Index

Features
32 GaN Technology In Audio Power Amplification
By Stuart Yaniger
As he reviews a Class-D amplifier and switchedmode
power supply (SMPS) evaluation kit from GaN
Systems, Stuart Yaniger details the benefits for audio
applications and shares his experiences with gallium
nitride (GaN) power semiconductors.

42 The Evolution of Production Line Rub & Buzz Measurements
By Steve Temme
This article follows the development of production line
Rub & Buzz detection, starting with the conventional
methods that, although developed 25 years ago, are
still valuable and well-used today, and ending with the
latest perceptual algorithms.

52 An Introduction To Testing Vacuum Tubes (Part 1)
Reasons For Testing Tubes
By Mark Driedger
If you are a fan of tube audio, sooner or later you
will need to test tubes. In this two-part article, Mark
Driedger examines why and how we test tubes.

56 Building a Guitar-Controlled Synthesizer
The Sample & Hold Time Machine
By Ethan Winer
This article is the first chapter of a fascinating DIY
journey that Ethan Winer takes through the world of
synthesizers. More specifically, a guitar-controlled,
all-analog synthesizer project that begins with a "time
machine" sample and hold section.

Columns
Sound Control
28 Frequency Response Of A Listening Room
By Richard Honeycutt
In this article, our audio expert argues that without
standardization of the meaning of "frequency
response" as applied to rooms, the term is probably
not a useful metric from an engineering standpoint.

Hallow-State Electronics
62 Amplifier Comparisons Revisited
By Richard Honeycutt
After years of research and much debate, our
columnist has determined that the superiority of
tube or solid-state amplifiers is truly a matter of
perception and is not necessarily a measurable or
objective difference.

Market Update — True Wireless Stereo Earbuds
8 The Next Frontier in Voice Technology
By J. Martins
As any developer working in true wireless stereo (TWS)
earbuds and hearables can attest, voice is a key feature
in such designs. From voice communications to voice
interfaces and voice enhancement, this article explores
the available hardware and software building
blocks for these product designs.

Edition Focus — Hearables in Focus
20 Putting The Smart In Smart Devices
The Future of Hearables Is Voice Controlled
By Probal Lala
Defined as ear-worn electronic devices, hearable technology
is at the intersection of wearables and headphones and
was designed for multi-purpose use, including voice
transmission, sound amplification, and wireless communications.


24 The Acoustical Challenges of Designing True Wireless Earphones
By Andrew Bellavia
Consumer expectations for true wireless earphones are
rapidly increasing, raising the bar on new designs.
This article from Andrew Bellavia of Knowles Corp.
explores the current trends as well as the acoustical
challenges and solutions for supporting them.

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