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Virtual Instrument Acquisition Examples

Introduction

This sequence provides a few different examples of how virtual instruments can be used in acquisition steps rather than using a typical stimulus plus Play & Record combination.  The benefits of using the virtual instruments include:

• Visual feedback during the acquisition – Users can monitor the data while it’s being acquired and watch for anomalies.
• Less steps in the sequence – Most of the same measurements can be performed with a combination of virtual instruments and post processing
• More familiar setup and controls for beginners – Engineers who are familiar with ‘bench-type’ instruments may prefer using the traditional setup of acquiring data using a signal generator and analyzer

This sequence uses a simple loop back on the Left channel of the sound card to make electronic measurements that illustrate the use of the various Virtual Instruments. Playback of noise and WAV files with the signal generator are acquired via the FFT and RTA instruments to show how the steps could be used. The sequence uses message steps to explain what is being done in each of the subsequent acquisition steps.

Example of Signal Generator and RTA Acquisition, and the resulting display

• The properties for the Signal Generator and Analyzer are set in the Acquisition Step editor.
• The Mode selection allows a choice from a list of presets for generating and recording the signal.
• Configure Record opens the analyzer that is selected under Mode. The resolution, weighting and record time values are set here.
• A custom name for the result can be entered in the Curve Name field.
• To set the stimulus type or select a WAV file click on Configure Generator. The level and duration for the stimulus is set here as well.
• More information on the Virtual Instrument controls can be found in the SoundCheck Instruction Manual.

Required Equipment

Software
SoundCheck 7.0 or later with the following modules: 2003 – Spectrum Analyzer (Scope-FFT)
2005 – RTA
2014 – Signal Generator
2015 – Multimeter
2022 – 2 Channel Acquisition (minimum of 2 channels of acquisition)

Hardware Setup & Calibration

Caution: This sequence is intended for use with a sound card loop back connection. Do not attempt to use it with a power amplifier. The signal level in the sequence is set to .5 Volts for all steps.

1. Use the appropriate Hardware Step values for your sound card.
2. The Hardware Default step in this sequence uses the Card Deluxe. If your system uses a different sound card, the Hardware Step settings must be updated.
3. Connect the left out to the left in as shown in Figure 1. (or Ch 1 out to Ch 1 in)

You are ready to start the sequence.

 

System diagram

Loop Back Example

Sequence Preview

The following is a breakdown of the sequence with examples of each step.

1 Loop Back Connection Message
Wiring instructions. Connect the Left out of the sound card to the Left In.

2 Signal Generator & Multimeter Message
The signal generator will output a 1 kHz sine tone, and the multimeter will measure the level.
The output level is 0.5 Volts. As long as the Hardware and Calibration steps are set correctly, the measured level should be approximately 0.5 Volts.
(The CardDeluxe will be down by 0.4dB due to the impedance difference between its output and input.)
The data is found under the Memory List - Value tab.

 

 

3 Generator Voltmeter Acquisition

 

 

 

 

 

4 Signal Level Limit

 

 

 

 

5 Multimeter Value Display

The Voltmeter value can be shown in a Table.
By using the Limit Step, the Voltmeter value can also be displayed in a Results Window, if this is preferred for printing.

6 Signal Generator & FFT Message
The signal generator will output a 0.5 V white noise signal.
The FFT will record the spectrum and place the data in the Memory
List.

 

7 WAV & FFT Acquisition
The stimulus will play for 5.1 seconds.
The FFT Analyzer will record for 5 seconds so      that the analysis is completed before the end       of the stimulus.
The Resolution is set to 50 ms, which will yield a spectrum of 1102 spectral lines. To get a record time of 5 seconds the number of averages is set to 100.
50mSec x 100 averages = 5 seconds

 

8 FFT Display
The FFT spectrum is reasonably flat with white noise.
Click Continue.

 

 

 

 

9 Curve Smoothing PP

10 Curve Resolution PP
The first Post-processing step applies a 1/3rd octave smoothing to the FFT spectrum. The second step changes the resolution of the curve to 1/3rd octave so
that it has fewer points.

 

 

 

 

11 FFT vs Smoothed Response Display
By using two Post-processing steps, we make a new version of the FFT Spectrum that has
been smoothed and reduced to a 3rd octave resolution.

Click Continue.

 

 

12 Signal Generator & RTA Message
The signal generator will output a 0.5 V white noise signal.
The RTA will record the spectrum and place the data in the Memory List.
The resolution of the RTA is set to 1/3rd Octave.

 

 

13 WAV & RTA Acquisition

 

 

 

 

14 FFT vs RTA Display
The FFT spectrum is reasonably flat with white noise.
The width of the CPB filters of the RTA increase as frequency increases. Since the level of the measured signal is proportional to the signal width, the RTA Spectrum increases in level as the frequency increases.
To avoid this, use Pink Noise when using the RTA.
Click Continue.

15 WAV & RTA – 1/3rd oct pink

16 WAV & RTA – 1/24th oct pink

 

 

17 RTA Display
The RTA is reasonably flat with pink noise.
Note that the 1/24th octave RTA is lower in level than the 1/3rd octave RTA.
The difference in level is again due to the difference in the width of filter between the two tests.
As the filter width becomes more narrow, the level in each filter band decreases.
Click Continue.

18 Speech & RTA Message
The signal generator is playing back an artificial speech WAV file at 0.5V.
The RTA is set to 1/3rd Octave.

19 WAV & RTA Acquisition

 

 

 

20 Speech Display
The Signal Generator plays a P50 artificial speech WAV file.
The resolution of the RTA curve is 1/3rd octave.

 

 

 

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To run the sequence in SoundCheck, please save the zip file to your hard drive, then follow the instructions in "Sequence Editor: Exporting/Importing a Sequence' section of the manual. Download Manual.