Frequently Asked Questions (FAQ)
- What sound card do you recommend?
- Which Data Translation module do you recommend?
- What Microphone do you recommend?
- What about microphone calibrators?
- Can I run the software on my Laptop?
- How do I connect the signal to the analyzer?
- What input signal levels can the analyzer accept?
- Do I need anti-aliasing filters?
- How accurate are the measurements?
- What sort of real-time update rate can I expect to see on my computer?
- How long of a recording can I make?
- What are the limitations of using sound cards for spectral analysis?
- What are the advantages of using the Data Translation modules?
- Why don't I hear any sound when using the post-processing mode?
- You offer several optional features such as the signal generator. Can these be purchased at a later time?
- How do I adjust the input gain using the Windows mixer?
- How does the copy protection work?
A) You can use the sound card already built into your computer; however, there are a wide variety of sound cards available that offer excellent performance.
A) Data Translation offers over 75 models with different channel count, sampling rates and special features. The DT-9837 is ideally suited for triaxial accelerometer measurements.
A) You can use the microphone compensation feature to work with a microphone which is not flat across the frequency spectrum. You can easily build the compensation table as long as you have a graph of the microphone's frequency response curve; contact us if you have questions about this. The microphones we recommend are complete with calibration data including a compensation table.
A) Microphone calibrators are essentially a device with a small loudspeaker element at one end of a cavity that also contains a 1 kHz tone generator. The end of the microphone is inserted into this cavity.
Calibrating SpectraPLUS-SC simply involves inserting the microphone into the calibrator and running the calibration utility. Enter the mic calibrator output level for the reference level (e.g. 94) and choose SPL as the reference units (rms). Now click the "Measure Input Signal" button and SpectraPLUS-SC will compute the calibration parameters; the analyzer will then be calibrated in units of SPL - it couldn't be much easier!
Calibrating SpectraPLUS-DT to a microphone can be done by directly entering the microphone sensitivity in mV/PA (included with the microphone calibration sheet), or by using the mic calibrator as described above.
A) Yes. Most laptops include built in sound support. USB and Firewire sound cards with excellent performance are widely available. All of the Data Translation DT-9800 models use a USB interface.
Q) How do I connect the signal to the
A) Simply connect the signal to be analyzed to the input connector of the sound card. Most cards feature a 1/8" stereo phone jack (tip/ring/sleeve). Professional grade sound cards offer XLR and 1/4" inputs
The DT modules have either screw terminals or BNC jacks depending on the model.
Q) What input signal levels can the
A) Sound cards are equipped with line level inputs which present a high impedance (>10K Ohms) load. The nominal voltage level expected is 1 Vp-p however, gain control (hardware or software) allows you to work with a wide range of signal levels.
The DT modules provide higher input impedance (>10M Ohms) and support selectable voltage ranges. 10 Vp-p and 1 Vp-p are most common. The DT-9805 provides a 20 mV range (500x) for weak signal measurements.
For high voltage inputs, an oscilloscope probe is recommended.
Some of the DT modules such as the DT9837 utilize Sigma Delta converters which provide inherent anti-aliasing protection. Depending on the application Anti-aliasing filters are needed when using other modules.
Q) How accurate are the measurements?
A) The frequency accuracy depends directly on the accuracy of the sampling clock on the A/D board. This is typically a fraction of a Hertz. The amplitude accuracy of the measurement is limited by the frequency response of the device. In addition,
The Data Translation modules provide calibrated outputs in volts or millivolts. This allows the transducer sensitivity to be directly entered for calibration purposes.
Q) What sort of real-time update rate
can I expect to see on my computer?
A) This depends upon the model and clock speed of your CPU, the selected FFT size, and the number and type of views open. To see for yourself on your own computer, install the software and take it for a 30 day test drive at no obligation.
Q) How long of a recording can I make?
A) A single wave file is limited to 2GB; however, the analyzer automatically rolls over and begins a new wave file when this limit is reached. This allows you to continuously record until the hard disk capacity is reached.
Please note that the storage required for each second of digitized audio data varies greatly with the selected sampling rate, precision and number of channels. To compute this, simply multiply the sampling rate in Hz by the number of seconds you will be recording. Multiply this by 2 if you are using 16 bit precision, and again by 2 again if you are recording in stereo. For example a 60 second recording at 44,100 Hz 16 bit Stereo will require 10,584,000 bytes (10.5 MB). By comparison, the same recording at 96,000 Hz, 24 bit Stereo will require 34,560,000 bytes (34.56 MB).
Q) What are the limitations of using
sound cards for spectral analysis?
A) Because the maximum sampling rate of sound cards is typically 44.1 kHz, your measurements are limited to 22kHz; however, there are a wide range of sound cards that support sampling rates as high as 200kHz. Sound cards have adjustable input gain - although this is helpful in many situations, it can get accidentally changed and does require that you provide a known reference signal if you want to calibrate the amplitude readings.
A) Calibrated inputs, up to 16 input channels, IEPE constant current for
powering microphones and accelerometers, DC coupling, TTL triggering, sampling rates
as high as 2.0 MHz, differential inputs, 500 volt isolation
between the inputs and the computer, Digital I/O lines for process
Q) Why don't I hear any sound when
using the post-processing mode?
A) In the post-processing mode, priority is given to spectral updates and the data is not played back through the speakers. For playback, use the recorder mode, or select a time segment from the time series display and use the playback segment commands.
Q) You offer several optional
features such as the signal generator. Can these be purchased at a
A) Yes, these options can be purchased at any time and can even be activated over the phone!
Q) How do I adjust the input gain
using the Windows mixer?
A) The Windows operating system provides a mixer utility for setting the input gain and output volume for each of the sound cards installed on the machine. To activate this mixer simply double click on the speaker icon located at the rightmost part of the taskbar near the clock. It can also be activated by clicking Start | Programs | Accessories | Multimedia | Volume Control,
or clicking on the Options | Device menu in SpectraPLUS-SC and clicking the Mixer button.
By default the mixer is titled "Volume Control" and shows a set of sliders for setting the output volume. Use the "Wave" slider to control the output level from the signal generator or wave file playback from the program. The left most slider controls the overall volume for all of the sources after they are mixed. A check box is also provided to allow you to mute selected sources. If you do not hear a signal, make sure that the volume levels are set properly and that it is not muted. Many users are confused by the line/mic sliders here and think that they are controlling the input gain; however, these sliders simply control how much of these sources are passed through to the output for monitoring purposes.
To set the input gain click on the Options | Properties menu. The dialog box will appear with options to allow you to customize the mixer, select which device to control, and to show/hide each of the various sliders. Change the "Adjust volume for" parameter from "Playback" to "Recording" and click OK.
At this point the mixer will change to show the sliders for controlling the input gain. The mixer title should show "Recording Control". Now adjust the various sliders to meet your needs. Make sure that unwanted inputs (e.g. microphone) are not selected.
Q) What is and how does the copy
A) This software is copy protected. All protection schemes impose themselves upon the user to some extent - our intent is to minimize this burden upon you, the legitimate user.
The copy protection mechanism requires an "authorization key" for permanent activation. Because this key is derived from parameters unique to your installation, we cannot provide this key in advance and you must contact our office after installing the software to obtain the key.
The procedure is simple:
- Install the software (you have already done this)
- Start SpectraPLUS by double clicking on the icon
- Start a 30 day temporary license. This will enable full operation for 30 days
- Select the License | Status and Authorization menu command and then Click on the "Authorize" button to bring up the site code dialog box (your site code will be unique to your machine)
- Click the "Copy to Clipboard" button and paste the Site Code into an E-mail and send it to our office at email@example.com
- When you receive the permanent "authorization key", return to this dialog box and enter it in the space below the site code and press the "Accept Key" button
Moving the program:
Because the Software Key is unique to your installation, copying the program will cause the license to fail. If you wish to move the program to another machine, simply install the program on the new machine and then transfer the license via a floppy disk or network connection. See the "Licensing" topic in the online help for details on transferring the license.
USB Hardware keys (also known as dongles) are also supported for those who prefer them - both single user and multiuser network keys are available.