I've struggled with latency on and off while tracking/recording through a mic either vocals or acoustic guitar.

It's probably not an issue for some, or others have solved what I've just done following their own exploration, or because they have a more expensive audio interface which just removes latency altogether.

But I've solved latency for me, and am passing this on in case any of the forum members have had issues with latency in their set up.

Here's what I've done and it's now perfect. (I have a small studio by the way, I'm not recording live bands).

1. I bought a microphone line splitter (ART SplitComPro). $35.00. Handles phantom power split issue.

2. Bought a mini mixer (Yamaha MG06X) with onboard reverb and delay. $120.00

Routing described here:

A. From microphone, mic line into the mic line splitter input.

B. One split line (the main one), route it to my audio interface mic input.

C. Audio interface output route to 2 channels of input on the mini mixer. This is for playback of the Sonar song's music tracks.

D. from the mic splitter, the second mic split line to an input channel on the mini mixer.

E. Set vocal track in Sonar to record enabled, but don't turn on input monitor.

F. Adjust on the mixer the balance between the Sonar music playback and the mic only channel (brought in by the split line). (Both sound absolutely clean).

G. Add some reverb from the mixer's built in reverb to the mic channel as desired.

H. Record.

Result? It's perfect!

The recording experience is perfect to my ear while performing/singing. The recorded audio track is perfectly clean and on time.

No more latency issues for me.

Solved for about $150.00 of hardware.

I started to type a message about MixControl, then realized the Scarlett may not have onboard DSP for reverb?

Correct. But it's not just about reverb. It's about zero latency, which I get with this. Previously I could have near zero latency, or whether it was a complicated song or whatever, some latency or pops could happen. With this method it's completely clean. Trouble free!

Good for my scenario. Hope it may help someone if they are frustrated.

TotalMix on the RME solves both issues, realtime monitoring and reverb/delay...
The only time this is not the case is when using an amp sim.
Then you have to rely on Sonar's input monitoring.
Tom

RME's are nice for sure. More expensive, but excellent.

Years ago... when "teching" a recording session in Nashville, we had to work this way (monitored straight off the console).
 
Back then, machines were significantly slower... and audio interfaces didn't have the extensive onboard routing/processing options that we now take-for-granted.
 
The only limitation is that you can't (obviously) monitor in realtime thru any software based processing.
ie:  No playing/monitoring in realtime thru AmpSim plugins/etc.
 
Most current generation audio interfaces have advanced routing/mixing capabilities (almost to the point of being a digital console "sans knobs/faders").
 
 
 
 

Yes, I'm sure the higher priced audio interfaces have advanced routing and at least near zero latency.

I'm specifically solving in my case for audio interfaces that don't have built in DSP effects, and specifically for capturing microphone recordings.

In my case, I have a Line 6 KB-37 which is an audio interface that allows me to get a zero latency experience with amp sim software (I use Amplitube 4) fully loaded with effects, hearing it with the effects, but recording the dry signal. This is ideal for me for amp sims. So I'm not using this external mixer approach for electric guitar monitoring.

I have three audio interfaces. They all work great for recording keyboards and MIDI performances. But for microphone recording, all three introduce some latency to one degree or another, even at low round trip settings. This external mixer approach (at a low cost) removes microphone performance latency altogether for me. Which is headache free, and trouble-free.

At least for my gear, this is the solution I was looking for.

Another trick is if you you have a direct monitor mode on your interface but no DSP, add delay/verb SEND on your recorder channel but have the channel itself muted during recording.   That way you can have zero latency feel plus FX and any latency in your verb/delay send will just make it sound like a bigger room.

That's a good tip.  
The added latency on the reverb is more pre-delay.

"another trick..." I've done/do that too.
Lawa has come up with an excellent/cost effect solution for his situation.
Just wanted to note that that RME's TotalMix is, as Jim stated, almost a "digital console".
One thing to consider when shopping for a new interface.
T