Audio Injector Ultra 2

(Last updated October 2019)

As the Cirrus Logic Audio Card is no longer available, options for recording ultrasound with the Raspberry Pi are unfortunately limited. There is a relatively new sound card available which is specifically designed to record ultrasound with a maximum sample rate of 192kHz: Audio Injector Ultra 2 from Flatmax Studios.

Instructions for setting up this card for use with a Raspberry Pi can be found here.

The card defaults to line input, so a simple bash script is needed to set up recording from the on-board microphones (Knowles SPU0410LR5H Ultrasonic MEMS microphones).

amixer cset name='ADC Mux' 0
amixer cset name='PGA Volume' 40
amixer cset name='ADC HPF Switch' 0
amixer cset name='ADC Soft Ramp Switch' 0
amixer cset name='Loopback Switch' 1

This can be saved as a bash script (e.g. record_from_mic.sh) and set to run at startup by adding the following line to /etc/rc.local just before exit zero (instructions on how to do this are here).

sh /home/pi/record_from_mic.sh &

Here’s the Ultra 2 Sound Card attached to a Raspberry Pi 3B+.  I’m only using the base card that comes with the AudioInjector sound card package, with a separate MEMS ultrasound microphone attached:

SoX can be used for sound-activated recording:

rec -G -c1 -r 192000 -b 16 -V2 /home/pi/temp.wav sinc 10k silence 1 0.01 1% -1 1.0 1% trim 2.0 3.0

These are spectrograms of bat calls from recordings made with the Ultra 2 sound card:

Nathusius’ Pipistrelle (2019-04-17 20:53:50)

Common Pipistrelle + Social Call and Soprano Pipistrelle (2019-04-18 22:36:09)

Soprano Pipistrelle (note feeding buzz) (2019-04-18 20:46:54)

Serotine (2019-04-18 21:42:12)

Noctule (2019-04-18 22:12:21)

Natterer’s Bat?

Soprano Pipistrelle Social Calls, possibly a juvenile (2019-06-21 23:34:03)

Serotine (lower) and Soprano Pipistrelle (upper) Calls (2019-06-29 00:43:17)

Noctule Social Calls (2019-07-1021:53:00)

Greater Horseshoe Bat (2019-09-27 01:42:13)

Social Calls – possibly Daubenton’s (2019-10-06 06:22:31)

I create a plot of the number of bat calls recorded each night, overlaid onto a map, showing the number of calls in the last 14 nights:

Bat calls are plotted each night and a updated on a map.

Between sunset and sunrise, the map displays a bar chart:

More details and results with this sound card will be added during 2019.