I got my system working using the National Instruments C API. As a result, I was able to grab 1000 records, each consisting of 20000 samples, to disk, in 10 seconds, for an average rate of 2 million samples per second. Each record corresponds to the signal received by a 5 MHz ultrasound transducer, and each sample is 16 bits wide. The effect is exactly the same as when one records from a microphone through a computer sound card, but 100 times faster. In fact, the instantaneous sample rate is 100 MS/s, which is more like 2500 times faster than a standard sound card.
It occurs to me that if I slowed down my data by a factor of 10000, each record would be eight seconds long and in the audible frequency. Maybe I’ll try that tomorrow. I suspect it will sound like a sonar ping in the movies, and that’s essentially what it is.
EDIT: Did I say 8? I meant 2. You can hear the sound if you like. It doesn’t sound at all like I was expecting. The transducer I’m using is deliberately wideband, but it wasn’t until I listened to the recording that I realized just how wide. If it were a narrowband transducer, it would sound like a bell, but instead it sounds like a wood block or a gunshot.