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In Unity's audio mixer

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the send and receive effects

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give us a great deal of control

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over how our signals are routed

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through the mix and particularly to effects.

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In this scene we have four game objects,

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each with an audio source and an audio clip

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loaded that's a loop of a music track.

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In our mixer we've setup two effect return tracks.

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These are normal groups which have respectively a reverb

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on reverb return and an echo effect

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on echo return.

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Currently they are not receiving

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signal from any other the other tracks in the mixer.

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But if we want to get a signal to them

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we can do that using the send and receive effects.

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Let's start with our arpeggio sound,

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which sounds like this.

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What we're going to do is that we're going to use

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a send effect to split the signal so that our

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arpeggio will continue to be routed

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through the master output but will

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also have a duplicate of it's signal

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with a controllable volume sent

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in this case to the reverb return.

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So first we're going to go to our reverb return track

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and we're going to setup our destination, our receive.

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We're going to choose Add - Receive.

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Now it's important to note that the

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sequence of these effects in the channel strip

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is very important.

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In this case the signal from the receive effect is

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coming in to the chain after the reverb,

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meaning that it's signal will not be processed

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by the reverb effect.

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What we're going to do is move the reverb down

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so it's in the chain after the receive.

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Now we're going to go to our arpeggio and we're going to

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apply a send effect, we're going to choose

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Add - Send.

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Now we'll see over in the inspector

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that we have a choice for what bus to route the send to.

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The term bus comes from the world of

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audio mixers in which a bus can be used

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to route signal from one channel

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to another or two multiple other channels.

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In this case the choice is between

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routing to a receive effect

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or to a duck volume effect.

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For more on duck volume effects

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check out the information linked below.

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We're going to choose our reverb return receive effect.

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Now we'll notice that a send level becomes visible.

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This is how much duplicated signal

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is being routed to the receive effect.

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We're going to start playing and turn that up

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so we can hear the effect happen.

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And you can hear when I stop it we get

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that nice reverb tail

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tailing off there because now the arpeggio sound

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has been routed through the receive effect,

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through the SFX reverb plugin

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and that's creating that nice cycle acoustic impression

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of our sound being played in a large space.

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What reverb effects do is they simulate

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the reflections of sound

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bouncing off of surfaces and returning to the listener

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in an acoustic space.

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Our synthesiser sound never occurred in an acoustic

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space so it has no natural reflection

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and we're adding those using the reverb effect.

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It's worth noting when we work with

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reverb effects via sends and receives

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that the dry level should be turned all the way down

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so that we don't duplicate the unaffected signal.

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It's also worth noting that the order

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of the attenuation and the send in our group is important.

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Currently the attenuation effect is before the send,

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meaning if we turn down volume

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using the attenuation effect the signal will stop

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passing to the send, let's give that a try.

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We can hear the trail trails off

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and the sound ends.

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If we reorder these effects we'll get a different effect.

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We're going to place the attenuation after the end

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and what you'll hear is that by

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placing the send before the attenuation effect

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the send is not going to have it's volume turned down,

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it will still receive volume

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before the attenuation turns the signal down.

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The result is that the send is going to continue sending

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signal out even though the main channel is turned off.

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What we can hear in this case is that whether or not

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the volume is turned down the send is still

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getting it's volume out to the reverb return

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and not what we're hearing is only

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the wet signal of the reverb

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coming back in to the main mix via the reverb return.

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This can be interesting for some non-traditional effects

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but typically you're going to prefer

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attenuation followed by your send.

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It's also worth noting as I mentioned earlier

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that if the receive effect is after,

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for example the reverb in this case,

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we're going to receive no effect, so it's important for any effects

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that you want to process your signal to be

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placed in the chain after the receive effect.

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Now one of the other major uses of sends

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is that we can use it to process

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multiple channels with the same effect.

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So in this track we also have

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a percussion element.

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And what we can do, by adding a send

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to that and routing that also to the reverb,

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we can add reverb, the same reverb

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to both of our tracks.

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So we can hear this gives us a very

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consistent psycho-acoustic impression,

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which is especially important if we're aiming for realism.

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To have things passing in to the same reverbs

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so that they feel like they're emanating in the same environment.

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It's also possible to use send and receive effects

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to route one signal to multiple effects.

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What we're going to do is we're going to send our

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arpeggio additionally to our

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echo effect on our echo return group.

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We're going to add a receive effect

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to the echo return and move it up in the

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chain so that it's signal will pass through the echo.

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Then on the arpeggio we're going to add a send

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and assign it's output to

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the echo return receive.

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once that's assigned we can test.

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And you can hear with that nice tail

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that our arpeggio is now being passed to both

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the reverb return and the echo return

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groups that we've created here via the two receive effects.

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What's great about this setup is that we can

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control the levels individually using the send volumes

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and we can really achieve a lot of flexibility

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in our mix this way.

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It's also worth noting that this is a common

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audio industry best practice because

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processing audio signals, especially with reverb can

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be very processor intense.

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Having a reverb on each of these tracks

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could have a serious CPU resource cost at run time.

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So minimising our use of effects

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by sending multiple effects to the same

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reverb on a return track

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is going to save us some CPU

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resources that we'll probably need elsewhere in our game.