Thanks @Alex Rogers for the handy explaination of some of these settings. I'm fairly new to the bat recording lark and I've been stumbling around in the dark a bit myself, so this is really useful. I have managed to capture some bat calls (only really Common Pipistrelle, so far) - but once I've gotten the hang of the settings, I intend to make recordings away from the back garden. I've been uploading my recordings to the BTO Acoustic Pipeline, for automated processing with some success - as hacking about with hours of recordings in Audacity is taking up way too much of my time. The Acoustic Pipeline can identify 24 species of European bat, plus small mammals and some insects and can be found here https://app.bto.org/acoustic-pipeline/public/login.jsp