I am learning about waveforms on analog vs. digital synths.  I have an oscilloscope that I am placing on each track that I would like to study.  I have learned that to hear the synth and the plug in to work in realtime, I need to turn the input echo on.  However, when I do this, I hear "doubling."  The way around that is that I just turn the fader for that track all the way down.
 
Is this the correct procedure (or the best way) of doing this?

When playing hardware synths connected to a Sonar (or any other DAW) MIDI track with input echo enabled on the track it is necessary to set the synth to "local off".

What that does is it tells the synth to go into "local control off" mode and ignore any commands made through it's own keyboard and other controls. Instead it sends the MIDI to SOnar which then echos the MIDI back to the synth and the synth then responds to the echoed MIDI.

Otherwise what happens in "local on" mode is you press a key and hear the note immediately, then as Sonar echoes the MIDI back to the synth you get the note repeated a few milliseconds later, which from what you say is what I suspect is happening here.

Another problem moight be audio latency if you are monitoring the synth's output directly either through the synth's own speakers, your audio interface or other amplification and also have the relevant audio track's input echo switched to on. In that case you hear the note once through the direct monitoring system and then again as Sonar echoes it back out delayed by whatever the system's audio latency is.

The answer to that is to only monitor the synth one way - direct or via Sonar, and if the latter get the audio latency down sufficiently for it not to cause a noticable delay in response to your playing.

Yes, normally you do need to enable Input Echo in order to hear in-the-box software synthesizers as you play them in real time from a keyboard controller.
 
However, this is usually not the case when recording outboard hardware synthesizers. In that scenario, you're going to monitor the external synth directly (so as to avoid latency) and enabling Input Echo would result in a second, delayed audio signal to be heard. 
 
There is a third scenario. If for some reason you do want to hear the results of in-the-box processing while playing an outboard synth in real time, then you'll want to silence the synth so all you hear is what's coming out of the fx bin in your computer. 
 
In your case, though, you don't need to hear anything. You're just looking at the oscilloscope. In that case, Input Echo is not necessary. (BTW, SPAN is another essential tool for what you're doing.)
 
 

bitflipper
 In your case, though, you don't need to hear anything. You're just looking at the oscilloscope. In that case, Input Echo is not necessary. (BTW, SPAN is another essential tool for what you're doing.)
 

 
I must have something set up incorrectly then.  I can only hear that hardware synth if either I 1) Enable recording and actually record, or 2) Enable the input echo
 
If I do not do one of those things, I can neither hear anything nor see anything on the oscilloscope.
 

tlw
When playing hardware synths connected to a Sonar (or any other DAW) MIDI track with input echo enabled on the track it is necessary to set the synth to "local off".


Another problem might be audio latency if you are monitoring the synth's output directly either through the synth's own speakers, your audio interface or other amplification and also have the relevant audio track's input echo switched to on. In that case you hear the note once through the direct monitoring system and then again as Sonar echoes it back out delayed by whatever the system's audio latency is.

 
This may be it - hearing out of the interface.  I have both synths into my Focusrite, and in the track I just have set those Focusrite as inputs.  
 
Guess I'm really confused.  

So if I understand correctly you have your external synths audio outputs routed to your Focusrite audio interface and you want to hear what you are playing as you record. If that is correct then the advice others have given you is correct.
 
To hear your synths as you play them you have to have your audio interface route the synth's audio to your speakers, or headphones, so that you can directly monitor the sound without it going through the computer. In this case you don't need the input echo on in Sonar because that would just echo what you are already hearing.
 
The other option is to not monitor through the interface directly but to monitor through Sonar and hear what you are playing coming out of Sonar into your audio interface. This is actually a good way to monitor if you need/want to hear effects used in Sonar as you play/record. However, this introduces some latency between when you play the sound and when you will hear it.  In this case you need to enable echo to hear what you are playing and disable any monitoring of the synths inputs directly by your interface.
 
It probably would help to draw you a picture but I am not in a place I can do that currently.

reginaldStjohn
 
The other option is to not monitor through the interface directly but to monitor through Sonar and hear what you are playing coming out of Sonar into your audio interface. This is actually a good way to monitor if you need/want to hear effects used in Sonar as you play/record. However, this introduces some latency between when you play the sound and when you will hear it.  In this case you need to enable echo to hear what you are playing and disable any monitoring of the synths inputs directly by your interface.
 

 
Got it figured out - I was monitoring directly through the Focusrite as well.  Seems simple enough, it just not occur to me.  Figured out how to mute that, and everything makes much more sense to me now.  Never realized the different ways of "hearing" what you are playing, and being able to A/B effects and such.  Cool stuff.  I'm new at all of this, but learning.  
Thank you all for responding.
 
As an aside, is there a way to view two plugins at the same time (Oscilloscope and Span)?

"As an aside, is there a way to view two plugins at the same time (Oscilloscope and Span)?"
 
You can put more than one VST effect in each effects (FX) bin.

By default, only one plugin has a display window. (This is the "recycle plug-in window" feature.)
You can change the default via Edit > Preferences > File - VST Settings to clear the Recycle Plug-in Windows check box. Or you can pin a particular plug-in window so it remains on screen when subsequent plug-ins are opened by clicking the window’s 'pin' button.