Aux Sends vs External Sends (Or: Do External Sends use more CPU?)

First of all, I really enjoy the flexibility that External Sends provide, as opposed to Aux Sends.
(-And perhaps this should go in the Ideas for Ardour category?..)

I don’t know if this has been changed since Ardour 6.9.0, but having immediate access to an External Send’s routing (via the “patchbay dialog” window) is excellent, especially in assessing where all the audio in the system is going to and from.

I noticed when trying to send part of a stereo signal to a mono bus via an Aux Send, it would automatically sum both the left and right channels into the mono bus without giving me the controls necessary to send either the left, or the right (or both) to the bus. As mentioned above, the External Send does give you this ability via its patchbay window.

So at this point I’m fine using External Sends for a lot of my odd routing (or a good portion of it), but I’m left with one big concern: CPU use.

- So will using External Sends instead of Aux Sends consume more CPU use? :question:
- Any other downsides or info. I’m not considering?

:+1: :v:

External sends are supposed to be used to connect to external applications or hardware, and not connect back to Ardour tracks/busses.

Otherwise you run into the same issues as using direct connections (ambiguous latency, no latency compensation - see On Delay Compensation & Recommendations for Routing)

Aux sends have two built-in delaylines:
  • The outbound signal can be delayed (when there are latent effects after the send).
  • The thru signal can be delayed (when sending to a bus with latent effects

There is also an additional delayline before the return on the target bus to align it with any direct signals that may be fed into the bus.

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Okay, yeah, over the past few hours I’ve just committed to using Aux Sends anyway, as they do seem to be faster/lighter overall, as well as easier/quicker to manage in general. (Deleting multiple External Sends at once seems to freeze my Ardour install.)

For stereo-to-mono situations, I will instead use stereo-to-stereo only and just mute one the channels if necessary.

Thanks. :wave:

Or if necessary use a mixer or stereo tools plugin before the send, and utilize the Pin connections to send a copy from it to the sends, and a copy that bypasses it on down the track. Does get complicated though if you do this a lot. In general probably easier to just stick with stereo busses in that case, but it is an option.


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