Sound Cards
Sound Cards
Sound Cards are by far the cheapest and most commonly used data acquisition device since nearly all modern computers are equipped with one.
Setting up a sound card
Setting up a sound card is easy. In the data acquisition dialog select “Sound Card” as the Data Source Type and a list of available sound cards will appear in the drop down list under the title “Select Audio Line”. Select the card you with to use and the number of channels (which can only be either 1 or 2).
Note that sound cards which have more than two input channels are likely to appear as multiple two channel devices and you will not be able to read out more than two channels at a time.
Notes and Warnings
Laptops
The audio quality of many sound cards is very poor and some, particularly those built into laptops which are prone to picking up electrical noise from the motherboard.
USB
Many external sound cards connect using USB. While convenient, we have often experienced problems with USB sound cards ‘dropping’ data. This happens more when the computer is busy (which it will be when you’re running PAMGuard). These drop outs can result in the lost of several percent of your audio input data.
If you are using a laptop and need an external sound card, try to get one that connects using Firewire (IEEE 1394).
Sample Rate Conversions
The Windows drivers in particular may make multiple sample rate conversions. this means that your beautiful high frequency data that you sampled at 96 kHz may be down-sampled to 48kHz and then up-sampled to 96kHz again without you knowing it. This will of course destroy all data at higher frequencies.
Some manufacturers provide alternative Windows drivers which you should use wherever possible.
If possible, test your sound card with a signal generator while viewing a spectrogram of the data to check that the high frequency data are OK
Unwanted, unexpected and unnecessary filters
Most sound cards are designed for human audio. Since we can’t hear much above about 15kHz (our children and pets may be able to do a bit better) some sound card manufacturers include a filter at around 20kHz and even if the software is allowing you to sample at high sample rates, you may not be getting any data through at high frequencies
Ideally use a sound card where the manufacturer has published a technical specification showing a flat frequency response over the range you’re interested in. As with sample rate conversions, test your sound card with a signal generator while viewing a spectrogram of the data to check that the high frequency data are OK
Calibration
Most sound cards do not come with calibration information.
If calibration is important, you’ll have to do this yourself. Note though that settings may change depending on any adjustments made to the computers audio settings (e.g. from the windows mixer).