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QuantAsylum QA401 User

’s

Manual

Page

38

One thing to keep in mind is that the Measurement Stop value sets the upper harmonic to be
considered. If you are looking at a 1 KHz signal, then a 20 KHz stop value means you will look at all
harmonics up to the 20

th

harmonic in your THD calculation.

But what if you have specified an 11 KHz signal? In that case, the second harmonic will be at 22 KHz,
which is beyond the 20 KHz Measurement Stop limit. In that case, the second harmonic will never be

seen, and the THD value won’t make much sense. In the example below, we can see a marker at 11 KHz

and 22 KHz, and since the Measurement Stop is set to 20 KHz the second harmonic is never seen.

THD Context Menu

The THD context menu is very simple, and allows you to set the Measurement Start and Stop limits.
Note these are the same limits that are set in the Power context menu. Additionally, you can specify
what will be used for the fundamental.

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Содержание QA401

Страница 1: ...QuantAsylum QA401 User s Manual Page 1 QuantAsylum QA401 User s Manual 192Ksps 24 bit Stereo Audio Analyzer Revision 1 704 January 2019...

Страница 2: ...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 ba...

Страница 3: ...cks 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 t...

Страница 4: ...d 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 Fu...

Страница 5: ...uts 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 Safe...

Страница 6: ...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...

Страница 7: ...ge 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 Feat...

Страница 8: ...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 inpu...

Страница 9: ...l 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 vo...

Страница 10: ...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...

Страница 11: ...e amplitude It should be 1 000Vrms 4 0 96 to 1 04Vrms on all 4 output ports of the QA401 This is a single ended measurement with one input to the DVM taken from the center of the BNC and the other inp...

Страница 12: ...sylum QA401 directory The file is named CalibrationData xml The contents of this file are parsed at startup of the QA401 application Once read the file isn t needed again until the next re launch So i...

Страница 13: ...t any time Re calibration will overwrite any existing calibration file Attenuator Adjustments The QA401 attenuator is built from 0 1 resistors and should be nominally 20 dB The software assumes it is...

Страница 14: ...e channel precisely The channel to channel variation is generally quite small 0 02 dB QA401 Basic Controls The QA401 application is shown below On the left side of the screen is the display area and o...

Страница 15: ...uickly adjust something like the offset knob If you hold down the ALT key while adjusting the mouse wheel the knob will spin 10 times slower than if no key were pressed This makes it easy to fine tune...

Страница 16: ...he dBV button for example has a dot in the lower left corner If we want to bring up a context menu related to the dBV settings we can click on that button while holding the control key down If a butto...

Страница 17: ...ops the analyzer acquisition although that can also be accomplished with the space key see the section on soft keys In the first picture below you can see the analyzer expanded to full screen and the...

Страница 18: ...o thinking that you are looking at test data from the device under test For this reason when you have selected to look at the output data you will be reminded with an on screen indication that you are...

Страница 19: ...s point it s important to highlight that the QA401 does not operate with constant stimulus tones The QA401 operates with stimulus bursts The reason for this is to ensure that the full transaction with...

Страница 20: ...inated mid cycle which might also result in a click or pop and it ensures the DC level is gently returned to zero Normally you ll be looking at the display with the following buttons pressed Freq Inpu...

Страница 21: ...FS levels are absolute there is no adjustments to be made via context menu dBV Context Menu The dBV levels are also absolute but in dBV mode we can specify whether or not external gains are attached t...

Страница 22: ...block as shown below The absolute peak levels are reported on the screen regardless of the Y Axis settings In the case below you can see the peak levels are also reported in watts because we specified...

Страница 23: ...a level of roughly 6 dBV coming into the analyzer If you specify that the peak level is 14 dBr then the display will indicate the same as the absolute value you measured with your DVM The next two bu...

Страница 24: ...and end display frequency The linear button also allows a center frequency and span to be set Recalling again the Axis controls the purpose of the default button is to permit you to zoom to your defa...

Страница 25: ...oomed Upon releasing the drag the new area will be zoomed You can pan around the display area by dragging with your middle mouse button Below you see a detailed zoom of the display Press the Default b...

Страница 26: ...e also accessed via the display context menu The simplest way to add a marker is to hover over the peak of interest and then press the m key or you can click the peak with the mouse Alternately you ca...

Страница 27: ...you can remove all the markers via the graph area context menu activated by right clicking in the graph area Markers details will show up in the display area This allows us to the see the frequency o...

Страница 28: ...y samples are averaged when the display values are computed Note that averaging doesn t change the noise floor but it does make it easier to see signals that might be buried in noise Since long averag...

Страница 29: ...frequencies the weighting works to attenuate the values below roughly 1 KHz and above 4 to 5 KHz or so On the QA401 weighting can be applied or removed by pressing the A weighting button or the Off bu...

Страница 30: ...oing this the extra half cycle that appears to immediately truncate will be suppressed The downside to this is that some other distortions will be introduced into the displayed spectrum But the introd...

Страница 31: ...ve is chopped off With windowing turned off Rect we see the resulting spectrum below Notice how much energy there is across the entire band even after 10 KHz This is due to the truncated waveform But...

Страница 32: ...t do we see then The response looks worse again What is happening It turns out that windowing functions are very complex and you should set them based on what you are trying to measure Any window opti...

Страница 33: ...ss a procedure calls specifically for this window you ll want to use Hanning Hamm The Hamming window is similar to Hann but with a bit more spectral leakage Generally unless a test procedure calls for...

Страница 34: ...nyq This is the root sum square or all components from the Nyquist Frequency down to but not including DC N Noise This is the non signal and non harmonic signals contained in the specified spectrum Mo...

Страница 35: ...n the plot below we can see a few key pieces of data related to this measurement First we can clearly see the measurement is performed over the 20 to 20 KHz interval Next we can see the total power me...

Страница 36: ...7 5V is applied this is roughly a 10 mA transient current In other words measuring a power supply s noise with an output greater than 7 5V requires special consideration The easiest way to solve this...

Страница 37: ...e can see this a bit easier below The THD function will sum the harmonic powers all the way up to the specified Measurement Stop In the plot above the sum of the harmonic power is 107 1 dB To go from...

Страница 38: ...armonic will be at 22 KHz which is beyond the 20 KHz Measurement Stop limit In that case the second harmonic will never be seen and the THD value won t make much sense In the example below we can see...

Страница 39: ...important it s important that you can readily see what the software has selected for the fundamental frequency Notice below that a small green F has been drawn near the X axis This way you can be cert...

Страница 40: ...highlighted numbers above The peak value is 10 dBV which is the level of the signal generator and Noise Distortion is measured as 95 5 dBV and thus this means the ratio of the signal to the noise and...

Страница 41: ...ple rate Farina Chirp This is an exponentially swept sine following the formula specified by Farina with a start frequency of 20 Hz and a stop frequency of 20 KHz regardless of sample rate White Noise...

Страница 42: ...se Looking at the input frequency we see a flat line at an arbitrary amplitude The amplitude depends on a variety of settings and the response of the DUT In the plot below we are in pure loopback mode...

Страница 43: ...an zoom in and see the loopback frequency response of the QA401 at 192Ksps In the plot below the 3 dB point is roughly 1 Hz to nearly 80 KHz This is easily measured by stopping the capture and then lo...

Страница 44: ...eraging both large FFT sizes and signal averaging As discussed above the impulse measurements are most helpful when characterizing circuits wired directly to the QA401 The white noise might be more us...

Страница 45: ...se frequency If you select Round to Eliminate Leakage then the frequency you select will be nudged a bit higher or lower to ensure that it sits precisely in the center of a frequency bin This will dra...

Страница 46: ...each value will change when you rotate your mouse wheel above the Freq and Amp knobs And again if you press the control key while adjusting the knob the knob will spin 10X faster And if you press the...

Страница 47: ...2 KHz etc As the marker shows the 1 KHz tone is roughly 100 dB below the input tones and thus the IMD shown is roughly 0 001 Another common IMD measurement is commonly known as the SMTPE IMD measurem...

Страница 48: ...he region of interest are the IM products around the 7 KHz tone Zooming in we can see these in great detail thanks to the high resolution FFT in the plot above Notice the 7 KHz 60 Hz harmonic is tight...

Страница 49: ...f the art today for LDOs is below 1uV in the audio band The safest way to measure the noise of a power supply is to use a resistor divider to drop the power supply voltage to under 5V For example if y...

Страница 50: ...e General dialog is used to adjust the system sample rates The 192 Ksps will be more demanding on hardware resources and as a result might not be usable on older or slower systems Display The Display...

Страница 51: ...vices that might have longer processing delays For example if you are testing a codec or a system that involves digitization and transmission reception then there could be 50 mS or more of latency in...

Страница 52: ...s by increasing the FFT size With the 1 50 release and later the ability to increase the pre buffer will permit the burst length to grow Keep in mind the latency compensation depends on the current sa...

Страница 53: ...re the output of a BNC relative to its outer conductor and you ll notice a slight offset around 1 or 2 mV By adjusting the output trim you can null that reading to very near zero The reading is shared...

Страница 54: ...know or calibrated and thus when you specify a tone level of 0dBFS the PC will generate a maximum valued tone 6 dBV will generate a half value tone etc Second the PC PC audio will start and stop along...

Страница 55: ...at 7 points per octave you d fill out the THD measurement as follows hit start test and the system could build a list of about 450 measurements to make and then make those measurements automatically...

Страница 56: ...king on a peak D This will delete all visible markers Deleting an individual marker can also be achieved by clicking on the marker Space This is the same as the Run Stop button Pressing this will togg...

Страница 57: ...r and confirm the driver is loading properly When you plug in the analyzer you should hear an audio indication that the analyzer has been plugged in If you do not plug in another USB device that is kn...

Страница 58: ...If the driver has not installed then you might have heard some tones indicating there was an issue or a message might have popped up explaining the problem You should see the device listed in the othe...

Страница 59: ...rectory of the installed location At this point the driver should install itself Step 3 Run the application and confirm it can connect At this point you have confirmed the drivers have been correctly...

Страница 60: ...QuantAsylum QA401 User s Manual Page 60 unplug and re plug the QA401 If it still doesn t connect then re boot your machine For problems beyond that please contact QuantAsylum support...

Страница 61: ...the QA401 from within the application This is helpful for performing swept measurements measurements that are repeated over and over with a single variable changing And example of a sweep is shown bel...

Страница 62: ...QuantAsylum QA401 User s Manual Page 62 If you d like to write a DLL plugin contact us at the support alias and we can provide some sample code...

Страница 63: ...ll shows up in the Visualizer menu menu list as shown below There is a DotNet interface embedded in the QA 401 executable that appears as below namespace QA400NS public interface IVisualizer string Ge...

Страница 64: ...e as follows 1 Using Visual Studio create a new project that is a DLL 2 Add a reference to the QA400 application 3 In your DLL class inherit from the QA400NS IVisualizer 4 Implement the required funct...

Страница 65: ...Otherwise the indicated settings file is loaded If indicated file name was successfully loaded then true is returned If the filename is empty then true is always returned and default is always loaded...

Страница 66: ...in degrees 180 to 180 The input signals must be sine waves of the exact same frequency The expected use of this function is as follows In situations where you are measuring a DUT using a single sine g...

Страница 67: ...be rounded up to the next power of 2 summary param name samples param void SetBufferLength uint samples void SetMuting QA401 Muting muteState summary Generates a continuous tone on the QA401 hardware...

Страница 68: ...personal computer or any other electronic device in your community Power Supply This device does not operate from line or mains voltage It is designed to be powered from a low power USB connection Ma...

Страница 69: ...QuantAsylum QA401 User s Manual Page 69 Appendix 5 Specifications See the QA401 Product Brief located on the QA401 product page on the QuantAsylum web site for the product specifications...

Страница 70: ...QuantAsylum QA401 User s Manual Page 70...

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