QuantAsylum QA401 User manual

QuantAsylum QA401 User’s Manual
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QuantAsylum QA401 User’s Manual
192Ksps 24-bit Stereo Audio Analyzer
Revision 1.704
January 2019

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Safety Notice
❖This device is not designed for working on potentially dangerous voltages.
❖This device is not designed for working on high energy circuits.
❖The maximum DC input voltage is +/- 5V into the device inputs.
❖The maximum AC input voltage is +/- 50V into the device inputs.
❖See additional safety notices throughout this document.
Limited Warranty
This product has a limited warranty for 6 months from the time of purchase. During this time, a device
failure that occurs under normal operating conditions will be replaced or repaired for free, not including
shipping. Generally, you will be responsible for shipping to us, and we will be responsible for shipping it
back to you.
Devices that have suffered a failure due to operation in excess of specified parameters can usually be
repaired for a nominal fee.
The contents of this document are provided “as-is” and may be changed or updated without notice. The
specifications on a particular product may also be changed at any time and without notice as we seek to
improve a product or improve availability of a product.
The limit of our warranty will not exceed the value of the product purchased under any conditions.

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S
Contents
Safety Notice.................................................................................................................................................2
Limited Warranty..........................................................................................................................................2
Legal..............................................................................................................................................................6
In the Box ......................................................................................................................................................6
Important Things to Know ............................................................................................................................6
Ground Reference.....................................................................................................................................6
BNC Input Voltages ...................................................................................................................................6
BNC Output Voltages ................................................................................................................................6
QA401 Output Voltage Offsets, Clicks and Pops.......................................................................................6
QA401 Analyzer Features..............................................................................................................................7
Analyzer Front Panel.....................................................................................................................................7
Front Panel Summary................................................................................................................................7
LEDs...........................................................................................................................................................8
BNC Inputs ................................................................................................................................................8
Understanding Differential Measurements..............................................................................................8
Rear Panel Summary.................................................................................................................................9
Electrical Characteristics of the Connectors .............................................................................................9
BNC Inputs.............................................................................................................................................9
BNC Outputs........................................................................................................................................10
USB Input ............................................................................................................................................10
Software Installation...................................................................................................................................10
X32 and X64 Installation .........................................................................................................................11
Calibration...................................................................................................................................................11
Verifying Calibration ...............................................................................................................................11
Calibration Adjustments .........................................................................................................................12
Attenuator Adjustments .....................................................................................................................13
QA401 Basic Controls..................................................................................................................................14

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Adjusting Knobs ......................................................................................................................................15
Adjusting Without a Mouse Wheel.....................................................................................................15
Context Menus........................................................................................................................................16
Control Overview........................................................................................................................................17
Run/Stop Button .....................................................................................................................................17
Display Options.......................................................................................................................................17
Axis..........................................................................................................................................................21
dBFS, dBV, and dBr Buttons................................................................................................................21
dBV Context Menu..............................................................................................................................21
dBR Button and Context Menu...........................................................................................................22
X Lin/X Log Buttons and Context Menus ............................................................................................23
Display Panning and Scrolling .................................................................................................................25
Titles and Markers ..................................................................................................................................25
Adding Markers.......................................................................................................................................26
Tracking Markers.................................................................................................................................28
Acquisition Control .................................................................................................................................28
Weighting................................................................................................................................................29
Windowing Functions .............................................................................................................................30
Measurement Types ...................................................................................................................................33
Definitions...............................................................................................................................................33
QA401 Measurement Types ...................................................................................................................34
RMS/Power.............................................................................................................................................35
THD..........................................................................................................................................................36
THD Context Menu..............................................................................................................................38
THD + N ...................................................................................................................................................40
Frequency Response...............................................................................................................................40
Generators ..............................................................................................................................................45
IMD Measurements ................................................................................................................................46
Power Supply Noise Measurements.......................................................................................................49
Settings........................................................................................................................................................50
General....................................................................................................................................................50

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Display.....................................................................................................................................................50
Other.......................................................................................................................................................51
Test Plugins .................................................................................................................................................54
Keyboard Shortcuts.....................................................................................................................................56
Troubleshooting..........................................................................................................................................56
Connectivity Issues..................................................................................................................................56
Appendix I: Test Plugins..............................................................................................................................61
Appendix 2: Visualizers ...............................................................................................................................63
Background .............................................................................................................................................63
Appendix 3: Software API ...........................................................................................................................65
Overview.................................................................................................................................................65
Appendix 4: Regulatory Notice ...................................................................................................................68
Overview & Safety ..................................................................................................................................68
Environmental.........................................................................................................................................68
Power Supply ..........................................................................................................................................68
Shock Hazard...........................................................................................................................................68
FCC ..........................................................................................................................................................68
Appendix 5: Specifications......................................................................................................................69

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Legal
This document and the associated computer codes, hardware design and hardware configuration files
are copyright © 2011 - 2019 by QuantAsylum USA LLC. All rights are reserved. You may share the
associated documents in PDF format freely. The EXE programs and code in the developer section is for
use only with QA products. The hardware and software designs are protected and the property of
QuantAsylum USA LLC.
In the Box
Your new analyzer should contain the following:
•QA401 Audio Analyzer
•Certain product variants may contain cables. But as a general rule, we’re moving towards NOT
shipping common cables with products any longer.
Installation software, this manual, and application notes for the analyzer are available on the web at
http://www.QuantAsylum.com. Inside the box you will find a card with a QR code that will take you to
our web page with the latest information on the product.
Important Things to Know
Ground Reference
The analyzer PC interface will share a ground with the PC. The audio inputs and outputs, however, are
isolated from the PC. This isolation is limited to 50V. Do not connect the QA401 to a product that has its
ground reference more than +/-50V from the PC ground.
BNC Input Voltages
The AC input to the analyzer should never exceed 56Vpp (single ended) or 28Vpp (differential). The DC
limits are lower. DC voltages above +/- 6V with the attenuator disengaged may permanently degrade
the performance of the device. In general, we recommend a DC limit of +/-5V regardless of attenuator
setting. If you need to measure power supply noise, see the section in the manual on how to safely do
so.
BNC Output Voltages
The BNC output connectors have a 47 ohm limiting resistor and thus have minimal protection. If you
accidentally connect a signal of more than few volts to the outputs, you may damage the output stage.
QA401 Output Voltage Offsets, Clicks and Pops
The QA401 output voltages will nominally have an offset of 1-2 mV. If you wish, you can trim those
offsets to microvolt levels through the Settings->Options->Other->Trim menu. However, be aware that
certain operations on the QA401 can generate clicks and pops and also modify offsets. This is especially
true when using external programs to control the QA401.

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Also, when changing the sample rate on the QA401, the codecs will be reset to ensure proper
application of their changed register settings. That will also generate a click or pop on the outputs.
Normally, these clicks and pops won’t present issues. But if you are working on very high-gain stages
with speakers or headphones attached, first take the time to familiarize yourself how the various mode
changes may impact your equipment under test.
QA401 Analyzer Features
The QA401 is our second-generation audio analyzer. Our goal in building the QA400 and the QA401 was
to leverage modern ADC and DAC codecs commonly used for audio analysis, while at the same time
eliminating some of the bigger problems that come with re-purposing audio ADCs for audio
measurement.
The QA401 Features:
•Stereo differential LEFT + RIGHT inputs
•Stereo differential LEFT + RIGHT outputs
•24-bit ADC and DAC
•Fully isolated from the PC
•Input attenuator and hardware-based overload protection
•USB powered
We hope you enjoy your purchase! Check back from time to time for new software updates, and drop by
the forum to say "hello" or ask a question!
Analyzer Front Panel
This section covers the various connectors on the analyzer and reviews the input and/or output
characteristics of these connectors.
Front Panel Summary
The front panel is shown in the picture below. From left to right, the following entities are explained.

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LEDs
Link LED This LED indicates the analyzer is connected to the PC and talking to the analyzer
application.
Run LED This LED indicates the analyzer is currently running (acquiring) data.
Atten LED This LED indicates the internal 20 dB attenuator is active. The attenuator is active when
the device is unpowered. However, try not to leave the QA401 connected to large
voltage swings while the device is unpowered. At higher voltages, it could damage the
unit.
BNC Inputs
There are two stereo inputs (Left and Right) and two stereo outputs (Left and Right). Each input and
output is differential. This means the magnitude of the + and –are signals are equal and opposite. For
example, if you were to look at the output signals on an oscilloscope, you’d see that when the L+ output
was sweeping a sine wave with a peak of +3V, the L- output would be sweeping a mirror image sine
wage with a peak at -3V. Differential signals are commonly used in noisy environments because
interfering signals that appear on both inputs simultaneously are “cancelled” and greatly attenuated.
However, for much of your audio work, you may prefer to use the device in single ended mode
especially if you are working on line level consumer audio type equipment.
If you wish to use the inputs single ended, then you could use a BNC terminator on the L- input, and
treat the L+ input as a single ended input. If you do not use the input terminator, then you will see some
thermal noise from the unused input resistor, which will raise the overall noise floor.
Understanding Differential Measurements
Differential measurements can create confusion even among very experienced engineers. Some
examples will help highlight the differences.
If you set the generator to 0 dBV and connect an Output+ to an Input+ and ground the Input-, then the
measured input will be reported as 0 dBV.
With the output set to 0 dBV, each output will measure 1Vrms on a DVM relative to ground (BNC outer
conductor). A differential measurement on a DVM (from Out+ to Out-) will measure as 2Vrms. This is
because the Out+ and Out- are 180 degrees out of phase with each other.
If you set the output to 0 dBV and connect both the Out+ and Out- connectors to the In+ and In-
connectors, then the QA401 measurement will show a peak of 6 dBV. This is because you are driving the
inputs differentially. This can be very confusing to first-time users: You are driving the inputs with 1Vrms
(0 dBV), and yet the QA401 is reporting 2Vrms (6 dBV). But this is precisely the same measurement
reported by the DVM when you placed the DVM across the outputs.
Keep in mind the QA401 inputs have no idea if you are driving a single input with 1Vrms and grounding
the other input OR if you are driving both inputs with 0.5Vrms. In both cases, you are hitting the ADC

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with the same differential voltage. That is, the differential input of the ADC is seeing 0.5Vrms on each
input in both cases.
Rear Panel Summary
The rear panel has a single USB connector. This is designed for high speed (480Mbps) USB connections.
The device consumes between 500 and 600 mA during normal operation. The device is not sensitive to
USB voltage variations.
Note that newer computers may employ very strict current sensing on the USB power flowing out of the
USB port. When the current exceeds a bit over 500 mA, the PC hardware might signal a fault.
If you suspect your PC has strict limits on the power, then you can use a USB Y connector. These are
connectors that plug into 2 USB ports and allow USB hardware to pull up to 1000 mA. One of the USB
ports has no data connection. It just takes power from the second port.
Alternately, most low-cost USB hubs that are self-powered do no sensing or limiting at all.
Electrical Characteristics of the Connectors
BNC Inputs
The 4 inputs pass through a 33uF series capacitor, followed a series 100 ohm resistor, and followed by a
resistor divider with a total impedance of 100K ohms. The corner frequency of this input network is
about 1.6 Hz.
The input DC blocking capacitor is polarized, with a 50V rating. The DC blocking capacitor can withstand
a negative voltage of 15%, or 7.5V, for 125 hours. In general, we recommend you limit the long-term DC
level (relative to ground) to just a few volts, keeping in mind that the capacitor will degrade over time
depending on the magnitude of the voltage.
The input stage will be clamped to the internal input rails (about +/-6.5V) through the 100 ohm input
resistor. The input attenuator is very fast. We’ve tested overload conditions of 70Vpp for hours on end,
with no impact noted to the performance of the device. During overload, the system will detect the
excessive input and engage the attenuator. After 1 second, the attenuator will be released, and the
input level again checked. This cycle will repeat indefinitely. Of course, the audible indication of the
relay clicking every second should alert you that the input voltage is too large and to manually engage
the attenuator.
IF YOU GOING TO APPLY A HIGH DC BIAS TO THE QA401 INPUTS, YOU MUST MAKE ABSOLUTELY SURE
THE ATTENUATOR IS ENGAGED. SEE THE SECTION ON MEASURING POWER SUPPLY NOISE COVERED IN
RMS MEASUREMENTS.
DO NOT EXCEED THE RATED MAX INPUT VOLTAGE OF THE Q401. IT CAN RESULT IN PERMANENT
DAMAGE TO THE QA401.

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NEVER USE THE QA401 TO MEASURE CIRCUITS THAT USE POTENTIALLY LETHAL VOLTAGES.
The default state of the input is that the attenuator is engaged. That is, when the device is unpowered,
the attenuator is active. When you first connect the device, regardless of UI setting, the attenuator will
remain active (attenuating). And when you close the QA401 application or unplug the QA401 hardware,
the attenuator will always re-engage.
DO NOT ROUTINELY LEAVE THE QA401 CONNECTED TO ACTIVE SIGNALS WHILE THE QA401 IS POWERED
OFF. ALWAYS DISCONNECT THE INPUT SIGNALS IF YOU ARE GOING TO POWER DOWN THE QA401.
BNC Outputs
The output op-amps have a 47 ohm series R in an 0603 form factor. If the output is accidentally
connected to a voltage more than few volts in magnitude, the 0603 resistor could act as a fuse and open
or the output op-amps could be damaged.
All 4 outputs are DC coupled, with a typical offset between + and –of a few millivolts. Beginning in the
1.5 release of the software, a trim function is provided to allow the user further null the offset. You
should be able to achieve a few 10’s of microvolts of offset between the differential outputs. See the
section on using the trim function for more information.
USB Input
The USB input is designed to operate with the maximum and minimum voltages specified by the USB
Implementers Forum, which is 4.75V to 5.25V. The noise performance of the analyzer should be
unchanged to down to 4V DC USB. Below that, certain regulators may begin to drop out and noise
performance might be impacted.
Do not exceed the 5.25V upper limit. Most hubs and equipment designed for USB will automatically
handle this for you.
Software Installation
Before plugging in your analyzer, you need to install the software. To do this, download the latest
installer package from QuantAsylum.com (see the Support → Downloads page) and run the installer.
Once installed, you may plug your analyzer into the USB connection on your computer.
The software no longer supports Windows XP, and we cannot help troubleshoot any issues you are
having with XP. Vista will probably work, but we cannot help trouble shoot any issues you are having
with Vista.
If you are running Vista or Windows 7 (32 and 64-bit version), the drivers should install automatically
when you plug your board in.