New Q

I don't understand what you mean with "digital to audio tracks" but any effect you place in an FX bin, ProChannel FX chain or on a clip has to be calculated in real time by your CPU. By definition that will take up CPU cycles. Various things influence how much;
1. How CPU intensive the plugin is (e.g. generally reverbs use more CPU than EQ and more recent plugins tend to be heavier than older ones). You could try substituting lighter plugs. 
2. How fast/recent your CPU is, not much you can do about this without getting a new computer.
3. The samplerate you're working at (higher samplerate=>more CPU), you could go down to 44.1KHz if you're at something higher. 
4. The buffer size/latency settings for your soundcard. With a good soundcard with proper ASIO drivers you can get buffer sizes as small as 64 samples or even 32 samples. This allows for incredibly low latency which is nice if you want to play aoftware synths or monitor through your DAW. But it also puts a lot more strain on your CPU than a higher buffer size. If you're in the mixing stage, you could try setting a buffer size of 512 or even 1024 samples. This means the computer will be slower to respond to real time input but during the mixing phase this is less of an issue and it will allow your computer to "look ahead" a bit more and spread out the needed CPU processing, leading to lower strain.

One way to remediate after the fact is to freeze those tracks as soon as you're done tweaking the recording and the effect settings.

Haha nm.

If I put the exact same effect on the fx bin of an audio track and a midi instrument track...the audio track tacks up vastly more cpu cycles.  That's what puzzles me.  (This is how my original question should have been framed, I apologize)
 
 

I realize it's counterintuitive, that's why I'm asking.   The audio track is usually mono, and the midi instrument tracks are usually stereo.  The midi instrument tracks use vastly less cpu cycles.  Same effect in both fx bins.  Maybe it has something to do with how they're routed through the master bus.  

eph221
Thanks bvideo, that's what I was looking 4.  But does freezing an audio track (one that you've recorded from a real instrument) really free up resources?  what does feezing actually do?!  I mean I kind of understand that the computer would then be working with an audio wave file instead of a midi file(?) but isn't that what the sequencer is using when you record a real instrument.  I think I may have some misconceptions that need clearing up.
 

Freezing is for freeing up CPU resources:

• In the case of an audio track with effects, a new audio file is created that has the effects applied. Now the DAW can just play the new audio file and no longer needs to use the CPU for those effects.
• In the case of an instrument track, an audio file is created by running the MIDI through the synth, with all effects applied. Again, the DAW now just plays the new audio file and no longer runs the synth or the effects through the CPU.

When you want to tweak a track that is frozen, unfreeze it first.

Yes it is audio fx not midi fx.  I understand the distinction, I think being a plebian from generation x means that I  look at the analogue and digital worlds a little differently.  A lot of the confusion comes from what sonar calls *midi instrument tracks* which are hybrid versus the straight up * midi tracks*. Anyways,  bvideo  thanks for the tip on freezing tracks that makes perfect sense, I'll just do that instead of trying to sleuth out the reason.

 
In the interests of minimizing confusion, a combined midi and audio track is a "Simple Instrument Track". 
 
It's simple because it occupies only one track visually, but in fact incorporates one midi and one audio track.  Exactly as if you set up one midi and one audio track separately for a soft synth.  In fact, you can easily convert back and forth between (1 midi + 1 audio) and 1 "Simple Instrument Track".
 
Normally, the Simple Instrument Track displays the midi track, but if you freeze the synth (converting the midi to audio) then the audio track is displayed, until you unfreeze.  I'm find them handy, others don't.
 
 

Thank you paul so what I was calling a *midi instrument track* in sonar parlance is a *simple instrument track*.  That's the hybrid thing, right? what's the regular instrument track that just records a wave form called?

I can see we're having problems with the LINGO!

There are also "Synth" tracks which are audio tracks that have a soft synth assigned as input (i.e. the audio half of an "Instrument" track that's been split). They get a different icon, have a Waveform Preview button in place of an Input Echo button.
 
I'd still like to have an example of an FX that uses more CPU on an audio track than on a synth/instrument track. I definitely cannot reproduce that.

Yes, that bothers me too, Brundlefly.  

I can't seem to reproduce this either eph221.  Now that you have your track types sorted,  are you certain you are not mistaking the additional overhead of the synth inserted in a simple instrument track for CPU load caused by the fx plugin? 

eph221
Bruce,  I read on another thread that someone's core 1 is maxing out.  Generally speaking that's what's happening to me.  I'll have about 8 tracks with fx  and sonar is just unusable.   My core 1 is spiking as well and I have 4 cores.  I have my buffers as large as they go on my tascam 2x2.  I did latency mon, and it appears I'm have overall issues with my firewire adapter.  Who knows.  It's going to take some sleuthing.  The original post though  of this thread is  true of old projects.  I'll see what happens when I record some new projects and let you know.  What's strange is that these are new issues for me,something I did recently is what's causing the issues.  But funny thing, the only thing I did recently was reset my computer!

The first core spiking has been mentioned in quite a few threads,  but a different issue to your OP.  I was referring to the variation in CPU load between fx loaded onto different types of track. Always confusing when there are a few issues in a single thread!  
 
With regards the first core CPU spike,  try disabling core parking.  I am running Windows 7 and it certainly solved that issue for me - though others not so much, so your mileage may vary. 
 
https://bitsum.com/parkcontrol/