EXTC-Stereo

From Radial Engineering:

The EXTC Stereo allows you to connect guitar effects pedals to the inputs and outputs of pro audio equipment such as recording interfaces and mixing consoles, so you can incorporate stereo pedals into your recordings and explore new creative possibilities.

The EXTC-Stereo gives you the ability to connect stereo effects pedals such as reverbs and delays to the line-level inputs and outputs of your console or recording interface. Use it to send drum overheads to a multi-tap delay, or breathe new life into a stale keyboard patch with a flanger or chorus pedal. Try it on vocals, strings, or any prerecorded track to add a new creative element to your mixes and revitalize your old pedal collection.

The EXTC-Stereo acts as the bridge between your recording interface and your stereo guitar pedals, making it easy to use your favorite pedal effects on any prerecorded audio tracks. The EXTC-Stereo converts the dry audio signal from line-level to instrument level for processing through your pedals, and then brings it back up to line-level to record the results.