audioXpress Magazine      March 2021

  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.

Comment
4 From The Editor's Desk
Audio Sensing In 2021
In just one year, communications, online commerce,
and the digital economy in general, evolved at an
accelerated pace.
Editorial By J. Martins, Editor-in-Chief

Features
46 The Science and Physics of High-
End Mic-Preamp Design (Part 2)
Minimizing Noise and Distortion While Maximizing Headroom
By Mike Meechan
In Part 1, Mike Meechan considered the fundamental
physics, which play a primary role in microphone preamplifier
design. Now he discusses its practical role and
how the mic pre-amp can retain the fidelity of the mic
signal along its path from transducer to output.

52 Clever Engineering
By Ethan Winer
One of the problems when designing large audio devices,
is the enormous amount of wiring that's needed. Wire is
expensive, and so is hand soldering all those connections.
In this article, Ethan Winer shows how electronic
engineers can reduce the number of wires using rotary
encoders, serial communications, and other solutions.

56 X-Altra Moving Coil/Moving Magnet RIAA EQ Preamplifier (Part 2)
MM Preamp, System Gain Amplifier, Filter, PSU, and Measurements
By Andrew C. Russell
In the second part of this article, the author details
the Moving Magnet EQ stage, system gain amplifier
and filters, along with the system's power supply unit
for the X-Altra design. The article concludes with some
measurements of the X-Altra preamplifier.

Columns
AudioScope
42 Very Low Distortion, Greater Than
400mA Output Composite Amplifier Headphone Driver
By Michael Steffes
Hollow-State Electronics

62 Souped-Up Practice Amps
By Richard Honeycutt

Market Update — Test & Measurement
8 Distributed Testing
Changing Processes for Remote Collaboration
By J. Martins
From research and development to production line
quality control, test and measurement instruments
and software are evolving from their traditional isolated
"bench" and "island" approach, into fully distributed resources.
This article reviews some of the key 2020 announcements on this front.

Edition Focus — Test & Measurement
24 QuantAsylum
A Real-World View of Test and Measurement
By David Logvin
Following the review of two of QuantAsylum's products —
featured in the December 2020 edition of audioXpress —
a lot of engaging information about the company and its
activities, inspired us to learn more. This follow-up article
provides an overview of QuantAsylum, its history, philosophy,
and product roadmap.

32 The Lab Bench of 2021:
Virtins Multi Instrument Measurement Software
The Research
By Stuart Yaniger
In 2015, Stuart Yaniger wrote a series of audioXpress articles
discussing how to adapt home computers and sound cards
for audio test and measurement. In this article, he experiments
with 2021 technology to see what sort of measurement
capability he can now achieve and updates his findings and
recommendations for our readers.

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