Testing the Sound Card: Task Four

1. This step checks the frequency response of the input section of the sound card. Close 002.pd, download the PureData patch 003.pd, and open it in PureData.

2. Press the "Start" button in the patch. The model is now waiting for track two to be played from the CD. This track plays a sine wave swept in frequency from 20 Hz to 20 kHz on a logarithmic scale. The sweep takes 60 seconds.

3. Start the playback, and watch the frequency response being plotted. The patch will stop automatically on completion. (If you are using a function generator, set it up to produce a 20-20K log frequency sweep in 60 seconds.)

4. The plotted line in the bottom chart shows the gain of the sound card's input section as a function of frequency. The optimal result is a flat line.

5. Note the highest and lowest amplification peak on your log sheet. This will give you a positive and a negative value.

6. The frequency response is usually specified as the the maximum and minimum deviation from 0 dB, i.e. 20 Hz - 20 kHz +0.1/-0.3 dB.

7. Some future RealSimPLE experiments may require a frequency response down to zero Hz (DC), which is available only on special data acquisition boards. For the time being, however, this is not a concern.