Rev Soft Inc's aa is a Synth Bass Sound Plugin that can be used with Perfect Piano and Walk Band. It is not a standalone app and requires Perfect Piano to be installed from Google Play. The plugin is designed to be used on Android 9.0 or higher devices.

To use the plugin, users need to enter the Keyboard Screen and select the switch instrument icon, where Synth Bass's icon will be displayed. Selecting it will automatically load the new sound.

It is recommended to adjust the sustain time through the app's settings to make the sound more comfortable. For any issues, users can contact the developer at