There are two effects sends. The first one is designed for the built-in effects. The second effect send is used for an external effect of your choice.
Next,
the DP-24 supports "insert effects" too. An insert effect is not controlled by the effects send1 knob.
Insert effects route your channel strip (track) into an available effect. This is a more severe effect and is probably less useful for vocals and more useful for a guitar. You must select the mode record, or play.
Next, there are dynamic effects that you can put on the input a-h. These effects are helpful, but will be recorded on your track.
The input section is genius because it allows you to use electronic cross connects. The input section has the option to be routed to a track or the stereo bus.
The thing to keep in mind is that for more control you will want to record your effects. Now, with an external effect, you can return it into the input section and route it to a track for recording.
If you want to record the built in effects, there are many options. But, in general, you could set up a pre fader send to effect 1. Then do a bounce. The send effect 1 (built in) is returned on the bounce bus. So, to record a nice effect that you can fully control later during mix down for vocals, set the effect 1 to Pre on the vocal track. Then turn the send knob for effect 1 on the vocal track to 100. Set the master effect 1 to 100. Why 100 and not all the way up? Because, anything over 100 will start to boost---that's not usually good.
Next, rewind your virtual tape to the start of the recording. Next, select bounce. Press the green select on the vocal track (the one with the pre send set to 100). Next, slide the fader all the way down to infinity on this vocal track. Why? Because you want to record 100% of the effect with no leakage of the real vocal track.
Next, hit the record button on the availabe destination track(s). It is best to use a single track unless you are relying on a stereo effect---like delay auto panning. In that case, you need to hit the red record button on two single tracks or just select one stereo track. If you use two single tracks, the lowest numbered track will be the left side. The higher numbered track will be your right side. Make sure you adjust the panning for playback.
Now, you are all set. Hit the record button. Now, what's happening is you are bouncing your vocal track to the destination tracks. But, since the vocal track fader is slid all the way down you are not really recording the vocal track. Instead, you are recording the return of the internal effects that is now routed to the bounce bus. In turn, the bounce bus is being recorded by the one or two tracks you armed. So, you end up with 100% effect only on your destination tracks.
Okay, after fully recording, get out of bounce mode by pressing the bounce button. Now, turn off the send effect on the vocal track and turn the effect send 1 on the vocal track to zero. Now, slide the vocal fader back up to where it sounds right.
What next?
Well, hit play and slide the faders up that were previously used as destinations for your bounce. Again, check the panning if you are using two single tracks. This will add your vocal effects that were just recorded.
Why did I do this?
Well, this frees up your effects to be used for something else in exchange for taking up 1 or 2 tracks. But, most importantly, this eases your workload during mix down. You can set the vocal effect, and increase or decrease it during mix down by moving the fader(s) of the effect recording.
This increases the number of effects you can have but it does take up 1 or 2 tracks. You can use the virtual track on the effects tracks to record different variation of effects. You can switch effects quickly during mix down by selecting the appropriate v-track when you need it.