QuantAsylum QA40 Series User manual

QA40x User Manual
Revision 1.20
February 2022

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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 +/- 50V into the device inputs.
✓The maximum AC input voltage is +/- 40Vrms into the device inputs.
✓The combined AC + DC must not exceed +/- 56V peak.
✓Do not apply any voltage to the outputs.
✓If the above are not clear, seek guidance from a person trained in electrical safety.
✓See additional safety notices throughout this document.
Limited Warranty
This product has a limited warranty of 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.
Legal
This document and the associated computer codes, hardware design and hardware configuration files are
copyright © 2011 - 2021 by QuantAsylum USA LLC. All rights are reserved. You may share the associated
documents in PDF format freely. The EXE programs and provided APIs codes are use only with QuantAsylum
products. The hardware and software designs are protected and the property of QuantAsylum USA LLC.

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Contents
..............................................................................................................................................................................1
Safety Notice.........................................................................................................................................................2
Limited Warranty..................................................................................................................................................2
Legal......................................................................................................................................................................2
Online Documentation..........................................................................................................................................5
In the Box..............................................................................................................................................................5
Important Things to Know ....................................................................................................................................5
Model Number..................................................................................................................................................5
Ground Reference.............................................................................................................................................5
BNC Input Voltages...........................................................................................................................................5
BNC Output Voltages........................................................................................................................................5
QA40x Output Voltage Offsets, Click and Pops ................................................................................................6
QA40x Analyzer Features......................................................................................................................................6
Analyzer Front Panel.............................................................................................................................................6
LEDs...................................................................................................................................................................6
Expansion Connector........................................................................................................................................7
BNC Inputs and Outputs ...................................................................................................................................7
Understanding Differential Measurements......................................................................................................8
Rear Panel Summary.............................................................................................................................................8
Electrical Characteristics of the Connectors.........................................................................................................8
BNC Inputs ........................................................................................................................................................8
BNC Outputs .....................................................................................................................................................9
Software Installation.............................................................................................................................................9
Windows Version..............................................................................................................................................9
USB Drivers .......................................................................................................................................................9
Calibration.............................................................................................................................................................9
Plugging in your Hardware..................................................................................................................................10
Button and Control Panel Operation..................................................................................................................10
QA40x Basic Controls..........................................................................................................................................11
Measurement Display Area ................................................................................................................................12
Trace Display Area ..............................................................................................................................................14
Markers...........................................................................................................................................................14

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System Annunciators......................................................................................................................................14
Control Groups....................................................................................................................................................16
Display Options...............................................................................................................................................16
Axis Settings....................................................................................................................................................17
Acq (Acquisition) Settings...............................................................................................................................19
Weighting........................................................................................................................................................20
Windowing......................................................................................................................................................21
Measurements................................................................................................................................................21
Generators......................................................................................................................................................23
Sine Generation ..........................................................................................................................................24
Multitone ....................................................................................................................................................25
White Noise ................................................................................................................................................27
Expo Chirp...................................................................................................................................................27
Full Scale Input................................................................................................................................................29
Run/Stop.........................................................................................................................................................30
Run/Stop Context Menu.............................................................................................................................31
Cursors............................................................................................................................................................32
Other Items.........................................................................................................................................................34
Soft Keys .........................................................................................................................................................34
Command Line Options ..................................................................................................................................35
Automated Tests.............................................................................................................................................35
Visualizers .......................................................................................................................................................35
Remote Control and APIs................................................................................................................................35

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Online Documentation
This manual focuses primarily on the functionality of the hardware and the software. The application,
measurement techniques and tradeoffs are a substantial topic especially when the experience level of users is
considered. Additional sources of information can be found at the Github Wiki for the QA40x, and the
QuantAsylum Forum.
In the Box
The box contains a QA402 Audio Analyzer. We do not ship cables with our products. The software for the
products may be downloaded from GitHub. The link for QA40x downloads is located here.
See the Github QA40x Getting Started Wiki for ideas on accessories.
Important Things to Know
This section covers some important details about the analyzer.
Model Number
In this document, the phrase “QA40x hardware”refers to the QA403 and QA402 hardware. The phrase “QA40x
software”refers to the application used to interface with the QA40x hardware. The family of hardware
products (QA402 and QA403 hardware) use the same QA40x software.
Ground Reference
There are two grounds to consider on the QA40x. The USB connection shares a ground with the PC, which in
turn shares a ground with the power distribution in your office. The audio side of the QA40x analyzer is isolated
from the USB ground: it is floating. When you connect the QA40x hardware to a device-under-test (DUT) to
make a measurement, you will need to establish a common reference point for the measurements. The DUT
will have its own ground (which may be similar to the PC ground). The isolation provided by the QA402 ensures
noise related to ground currents is eliminated.
If your DUT is also floating (which is common if the DUT is powered from a “brick”-style wall adaptor, then you
can reduce powerline hum in your measurements by connecting the floating ground to an earth ground.
BNC Input Voltages
The inputs on the QA40x hardware are designed for AC inputs, with some DC present. The DC will be blocked
by the input capacitor and cannot be measured. DO NOT EXCEED THE SPECIFIED LIMITS, OR YOU WILL DAMAGE
THE QA40x AND/OR MIGHT INJURE YOURSELF.
BNC Output Voltages
The BNC outputs are DC coupled. They cannot withstand inadvertent connections to DC voltages where more
than 10 mA of current might flow. Extended shorting of the outputs will result in an increase in temperature
of the output stage, which can cause a permanent shift in performance.

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QA40x Output Voltage Offsets, Click and Pops
The QA40x outputs may exhibited DC offsets up to +/- 2 mV or so. Additionally, operations such as sample rate
changes may generate momentary clicks or pops. If you are working on very high gain stages or driving a power
amp that is driving a speaker, be aware that these offsets, clicks and pops might impact your DUT.
QA40x Analyzer Features
The QA402 is our third-generation analyzer, and the QA403 is our fourth-generation analyzer. They build on
the QA401 by adding additional input and output handling in addition to a front-panel expansion port.
The QA402 and QA403 features:
•Stereo Differential Left + Right Inputs
•Stereo Differential Left + Right Outputs
•24-bit ADC and DAC for QA402, and 32-bit ADC and DAC for QA403
•Fully Isolated from the PC
•8 Input Gain Stages, from 0 dBV to +42 dBV full scale (the maximum input is +32 dBV)
•4 Output Gain Stages, with a maximum output level of +8 dBV (single ended) or +14 dBV balanced.
We hope you enjoy your purchase. Our forum is a great place to learn more about how to use your new
analyzer, or you may contact us at [e-mail]. We welcome all questions, no matter how
simple. Analyzers are complex products, and your questions help us improve our products.
Analyzer Front Panel
The front panel of the QA402 analyzer is shown below. The QA403 is similar.
From left to right, the following elements are described below:
LEDs
There are 3 LEDs that glow green when active.
Link LED: This indicates the QA402 is “talking” to the desktop application software.
Run LED: This indicates the QA402 is running an acquisition.

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Atten LED: This indicates the QA40x input attenuator is active. If you are going to connect the QA40x hardware
to large signal, it is best to pick one of the higher input ranges that enable the input attenuator as you attempt
to learn the characteristics of the signal you are measuring. This is especially true if you are measuring
equipment that is being repaired that might have potentially unexpected outputs behavior. The LED allows you
to readily see if the input attenuator is active, ensuring the QA402 can protect itself from unexpected inputs.
Expansion Connector
The QA403 and QA402 have slightly different front-panel connector pinouts. The expansion connector for the
QA402 is a 2x8 pin male connector with a 1.27 mm pitch. As you face the connector and front-panel, the
connector pin out appears as follows:
The front-panel connector currently supports driving Generator 1 and/or 2 DAC output sines at 16- or 32-bit
widths at 48 kSPS. I2C, ADC input, and sample rates other than 48 kSPS are not currently supported, but may
be added in the future. More information and schematics for use with the front panel expansion connector
can be found on the QA40x.
BNC Inputs and Outputs
The QA40x hardware has 4 outputs, or both left and right differential pairs. The + and –signals are always
complementary. That is, when the L+ signal is rising, the L- signal is falling. Viewed on a scope, the + and –
signals are always moving in equal but opposite directions.
The left and right outputs largely work in unison, but there are certain modes (for example, muting or external
waveforms from an API) where the left and right outputs can work independently.
Most consumer gear will take a single-ended input and output signal. Pro-audio will often take a differential
signal. Differential signals are commonly used in noisy environments because interfering signals that appear
on both inputs simultaneously are “cancelled” or at least 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 can use a BNC terminator

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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- via BNC terminator, 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 (the 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 -10 dBV and connect both the Out+
and Out- connectors to the In+ and In- connectors, then the QA402 measurement will show a peak of -4 dBV.
This is because you are driving the inputs differentially. This can be very confusing to first-time users: You are
driving the inputs at 316 mVrms (-10 dBV), and yet the QA402 is reporting -4 dBV. But this is precisely the same
measurement reported by the DVM when you placed the DVM across the outputs. Keep in mind the QA402
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 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 700 and 900 mA during normal operation. The device is not sensitive to USB voltage
variations, but it can be sensitive to USB voltages that fall below 4.6V as measured inside the QA402. For this
reason, use USB cables that are short and have 24 AWG power conductors. You can often read the wire gauge
directly off the side of the USB cable. Note that some computers may employ very strict current sensing on the
USB current flowing out of the USB port. When the current exceeds 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 audio signal inputs passthrough a 4.7uF series capacitor, followed a series 470 ohm resistor, and followed
by a shunt resistor divider with a total impedance of 100K ohms. The corner frequency of this input network is
about 0.4 Hz. The input DC blocking capacitor is an aluminum electrolytic non-polarized, with a 50V rating.
Keep in mind that aluminum electrolytic capacitors have limited lifetimes that is dictated by their stress and
temperature. These lifetime specifications are usually at high ripple currents and high temperatures, which
won’t be seen by the analyzer. But it’s a good idea to not leave large signals or high DC values connected to
the analyzer overnight if you are not actively measuring something.

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Excessive input voltages can also stress the 470 ohm input resistor. The purpose of this resistor is to limit
current in fault conditions, and it’s a special composition resistor that can cope with very high pulse currents.
But under extreme conditions the resistor might open to protect the inputs.
BNC Outputs
The output op-amps have a 100-ohm series R in an 0805 form factor. If the output is accidentally connected to
a voltage more than few volts in magnitude, the 100-ohm resistor could act as a fuse and open or the output
op-amps could be damaged. Do not short the output stages. Do not drive the output stages into loads that are
below 100 ohms or so, especially at higher output levels.
Software Installation
The QA40x application has an installer, but it can also run from a USB key without any installation (although
certain support files such as this help document won’t be present when select Help->Open Users Manual PDF).
Windows Version
The QA40x application was developed on Windows 10, although it might run on previous versions of Windows.
USB Drivers
On Windows, you do not need to install drivers. The hardware uses special USB descriptors to tell Windows to
use a WinUSB driver. The first time you plug the hardware in, Windows should automatically load the drivers.
When successfully installed, you should see the QA402 (or QA403) appear in the USB Devices section in
Hardware Manager
Calibration
The QA40x hardware was calibrated at the factory and should deliver +/- 2% accuracy across all input and
output ranges. If you measure the QA40x outputs with your DVM, keep in mind that DVMs are generally
specified at 50 or 60 Hz and their accuracy at 1 kHz and higher is degrading quickly. A better solution for
confirming accuracy is a benchtop DVM. These will typically have +/-0.05% accuracy for signals up to 20 kHz or
so.
When measuring the QA40x outputs, remember the QA40x hardware uses bursted outputs for measurements.
See the description of the IDLE button for times when you need a non-bursted stimulus. This can be useful if
you are checking DUT gains manually with a DVM.

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Plugging in your Hardware
The QA40x application requires you to specify the hardware model you are connecting. In the lower left of the
application, you will see a message indicating which hardware is expected. You can change that in the File->
Device menu option.
When you have correctly set your device and plugged the device in, you will see a status confirmation as shown
in the lower left corner:
After the device has been connected, you can begin making a measurement by pressing the RUN button in the
Run/Stop control group.
Button and Control Panel Operation
The buttons in the control panel on the left side of the screen are large enough to be easily pressed with a
finger if you are using a touch screen. The control panel can be scrolled up and down with the mouse wheel. If
you are using a trackpad, there is usually a trackpad shortcut for mouse wheel operation. Usually this is a two-
finger drag across the trackpad.

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Alternately, you can use the up/down arrows to scroll the panel normally, or page up/down to scroll the panel
more quickly.
The buttons will illuminate when the mouse passes over the button unless the button is disabled. This gives
you a chance to better read the text when is normally dim when the button is in the un-pressed state. When
the button in pressed, the text and the perimeter will illuminate.
Some buttons are part of groups, and groups might only allow a single button to be pressed at a time. The
sample rate buttons are examples. When you press a button that is part of a group that only permits a single
selection, the button that is currently illuminated will momentarily flash to signify it is turning off in response
to your request to change modes.
QA40x Basic Controls
The QA402 and QA403 application, also known as the QA40x application, is shown below:
On the left side of the application is the CONTROL region. On the right side of the application is the SPECTRUM
or GRAPH region.
In the control region, you can use the mouse wheel to scroll the control set up and down. On a laptop, this can
usually be done by using two fingers on the track pad (check with your laptop vendor to see how they
recommend emulating a mouse wheel if the two finger technique doesn’t work). Alternately, the Page Up and
Page Down buttons will scroll the control region, as will the up and down arrow keys.

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Measurement Display Area
At the top of the trace display is the measurement display area. Measurements can be added by clicking in this
region:
Clicking will bring up the Add Measurement dialog box:

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You can filter on measurements by entering text in the Filter Measurements dialog. For example, if you enter
“thd” (case insensitive) the test choices will collapse to the following:

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If you wish to add a title to your graph, that can also be done in the Add Measurement dialog in the text box
at the bottom of the dialog. You can specify up to four lines of 80 characters each.
Trace Display Area
The graph display area can have a few areas of added information, in addition to the measurement traces.
These are highlighted below by the red boxes. On the left are the system annunciators. On the right are the
markers.
Markers
Markers can be added to the plot by right clicking on a peak. The markers are always sorted from highest
amplitude, and the tabular display will convey both absolute value and relative value referenced to marker 0
(the highest peak).
Markers can be removed by right clicking on the graph and selecting “Remove all Markers” or by pressing the
D key.
When placing markers on tones that are close in frequency to other tones, it can be helpful to click and drag a
zoom window, place the marker, and then zoom back out.
System Annunciators
System annunciators are short messages to convey special modes of operation, and they will appear in the
upper left corner of the graph. The complete list of annunciators that may be displayed are below:

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ADC Overflow: Indicates the ADC had packets, but the USB didn’t take them in time and so may have been
lost. Sometimes, this message can be a bit pessimistic and what was flagged as an error might not have been
an error. When this message appears, either re-acquire the signal or carefully inspect the time-domain signal
for a dropout.
Atten: Indicates the front-end attenuator is active.
DAC Underflow: Indicates the DAC needed packets, but the USB hadn’t delivered them yet. Sometimes, this
message can be a bit pessimistic and what was flagged as an error might not have been an error. When this
message appears, either re-acquire the signal or carefully inspect the time-domain signal for a dropout.
FFT Too Small: Indicates the FFT might be too small for the displayed activity (usually this will be shown in
Frequency Response (FR) mode).
FP I2S Clip: Indicates the signal being sent to the front panel is clipping.
FR Gain: Indicates the FR mode graph is showing gain instead of absolute level.
FR Ref R: Indicates the FR mode graph is using the right channel for the reference.
Input Gain: Indicates the user-specified input gain.
Latency Compensation: Indicates the user-specified latency compensation. Often, when working with
Bluetooth or other DSP-based equipment the latency compensation will need to be increased to ensure the
signal is properly captured (see Edit->Settings).
Mirror: Indicates Generator 1 settings are being mirrored to the PC’s primary audio device.
Mute L: Indicates the left channel is muted.
Mute R: Indicates the right channel is muted.
No Channels Selected: Indicates no data has been selected for display. Select L, R or both.
Caution! Input Range Test Mode: Indicates the input level is unclipped and can display levels in excess of safe
operation. This also indicates the front-end attenuator is always active. This mode is used for testing by
authorized personnel that need to verify measurement accuracy at higher voltages.
Output Gain: Indicates the user-specified output gain.
Output Displayed: Indicates the output traces are being displayed, rather than the input traces.
Range: Indicates that during the last acquisition and overload was encountered and the attenuator was
engaged.
Pause: Indicates a non-zero user-specified pause time has been entered (see Edit->Settings). This pause will
occur between acquisitions and can be helpful in dealing with higher latency systems OR in systems where you
want to careful limit the average power delivered to a load (by making measurements less frequently).
A Weighting: Indicates A-weighting has been applied to the displayed trace.
User Weighting: Indicates the user-specified weighting has been applied to the trace. This will also include the
file name of the weighting file.

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Control Groups
The control panel on the left side has several groups of controls. Inside each group, there are two control types.
We can see an example of this in the Axis Settings control group. On the left side you can see four buttons, and
on the right side you can see a pair of up/down controls.
The up/down controls allow you to increase or decrease a quantity. They are sized for fingers on a touch screen,
but you can also click them with a mouse.
The buttons on the left side are also sized for a finger on a touch screen. Note some buttons have an underline
beneath the button label. That indicates a “context menu” is available for that button. To active a context
menu, you can either:
1) Click (or touch) and hold. After 1 second, the menu will open. This is useful if you are using a finger on
a touch screen.
2) Mouse right click. The menu will immediately open.
A sample control “stack” is shown below. The heavy underline indicates the dBV and X LOG button both have
a context menu available.
Display Options
The Display Options control group is shown below:
The Time and Frequency buttons will toggle between the time and frequency domains. If you press the time
button, you’ll see a trace that shows input and output waveform, with volts as the Y axis and time for the X
axis.
The Input and Output buttons allows you to toggle between displaying what is being output to the DAC or to
see what is being captured by the ADC. This is useful for letting you see the impact the DUT has on the
waveforms.
The Left and Right buttons allow you to pick which traces will be displayed. Left is always shown in Yellow and
Right is always shown in Red.

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Axis Settings
The Axis Settings control group is shown below:
The dBV button will display the frequency domain in the absolute units of dBV, while the dBr button will display
the frequency domain relative to a signal you specify.
The context menu for the dBV button is shown below:
In this dialog, you can specify the units for the Y axis. Normally, dBV is used. But you can also specify dBu. You
can also specify if you have any external gains being used. For example, if you have a mic pre-amp of 20 dB,
then you could specify 20 dB of input gain and then the display would show you an input-referred noise
measurement (for example).
The dBr context menu is shown below:

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When using the dBr display option, you need to specify your reference amplitude. This dialog allows you to
quickly specify the reference using the display peak or the left measured at 1 kHz. Or you can specify the dBV
value that should map to 0 dB. Or you could specify the level in dBr. This is useful if, for example, you know
that a mic should generated a certain output at a given sound pressure level.
When using the dBr setting, you can also override the Y-Axis units and specify your own units (for example,
dBSPL).
The “X LIN” button enables a linear display on the X axis. In this mode, all frequencies are equally spaced. The
context menu for X LIN is as follows, and it allows you specify the start and stop frequencies.

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The “X Log” button is similar, except it selects a logarithmic X axis. The dialog box options are similar.
Acq (Acquisition) Settings
The Acquisition Settings control group allows to set FFT sizes and averaging.
Larger FFTs will take more time to acquire. Generally, it’s good to work with an 8k to 32k FFT for most work.
Some measurements, such as THD+N will show little benefit at higher FFT settings. But other measurements,
such as THD, will indeed show marked improvements at larger FFT sizes as the noise floor is reduced and
harmonics are revealed.
Each click of the averaging button will increase or decrease the average count by one. If you click while pressing
the CTRL button, the count will change by 5 counts.
When averaging, you might wish to re-start the averaging process for some reason. That can be done with the
Reset button. Whenyou change input levels or other certain other parameters, the averaging will be re-started.
When you activate averaging, a measurement tile will automatically be added showing the averaging status. In
the example below, we can see averaging has been set to 10, and we’ve collected 3 of the 10 waveforms so
far. As you reach the specified numbers, the display will show 10/10 for all subsequent measurements. This
indicates the averaging buffer is full and what you are seeing is the full averaging taking place.

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Weighting
The Weighting controls allow to you apply standard “A Weighting”, or a custom User-weighting function. The
latter can be useful for “flattening” an RIAA response curve, notching out undesired frequencies or
compensating for known DUT deficiencies.
The context menu for the USER1 weighting is shown below: