Here goes another (I hope, cuz they're easy) dumb question. I am trying to learn the ins and outs of MIDI and some have indeed got me perplexed. While recording a single midi track with a single softsynth through a single audio track, halfway through the piece the audio dropped out. No one here but me and I didn't touch or bump anything but the keyboard of my FanX. I continued to play, with no audio, thinking that the midi information would still be recorded and as long as I give it to something that can play it I'm good. Upon reviewing the MiDI track at the time I lose audio there is a line that has stayed continuous just above the dots and dashes suddenly it starts to fall off in pieces tied together with the little dots I think are called 'nodes' when I see them in the automation lane. Now, I was playing/recording so I had no automation enabled and there is no change in the line when I reviewed the automation lane. It would be great if I could just pick up this little 'node and put it back where it goes but I think that falls into MIDI editing which I haven't tackled yet. Is it possible to get my sound back, and does anyone know what happened and why?

Note: I notice I the 'event' list it is seen as a 'shape' that is 'linear', whatever that means. the event seemed to be recorded at each change in the little node on its way down to the bottom where there is no sound. Poor little node, must be an awful place to be...

Two suggestions.

The first is to go into preferences and adjust the MIDI (not audio) buffer. By default it's set to 250ms which is too low for many systems/setups. It tells Sonar how far ahead to read MIDI tracks and if the buffer is too small it gets full then overflows which can cause all kinds of MIDI strangeness. Try 500ms and if that doesn't help 750.

Secondly, are you sending any MIDI continuous controller commands (CC) from the keyboard? Examples would be the mod and pitch wheels, aftertouch and touching any control on the keyboard itself. Depending on the settings in the synth they might do all kinds of things, including altering volume. There's also the possibility that the keyboard might be glitching and sending CCs without you realising it.

The line and nodes is an envelope of some sort. It might help to know which CC it is. CC7 for example is usually used to control volume. Sonar doesn't randomly generate envelopes or MIDI CCs so something somewhere is creating them and Sonar is then recording them.

It might help downloading MidiOx, which is a free tool that's usefull for diagnosing MIDI issues. It can tell you what MIDI commands are happening and where they are coming from.

I'll give Midiox a try , Thanks so much! My midi buffer had been set due to prior advice to 1024, not sure just why that exact number but I got it from somebody. I'm playing a Fantom X8 that indeed has a ton of commands at its disposal, none of which I'm all that savvy of other than the 88 little black and white switches up front that I enjoy so much! Thanks again for the direction!!

Some soft synths or even some instruments that load into something like Kontakt, do weird things with regard to midi volume or pitch, or other aspects of the sound, and it can be QUITE maddening to debug and resolve.
 
I found that some soft synth components of Native Instruments Komplete 8 Ultimate by default have their master volumes tied to CC 11 midi messages - that is something I would never myself do, but it's how a bunch of their components and some individual presets within a given synth are set up.
 
Certain loaded presets for certain loaded Ensembles in Reaktor 5 have pitch tied to the modulation wheel - which until I figured it out drove me NUTS for almost 2 weeks.
 
I used the above only as examples of some of the weirdness that does exist out there with soft synths, so let's  start by figuring out exactly which synths and which presets you are having these issues with.
 
Oh, another thing that could be at play here is some of the Sonar settings, like that midi buffer setting talked about above (250 ms being too small for some folks, etc).  The default setting for that used to be 500 ms, but in one of the X releases of Sonar, it got changed to now default to 250 ms.  Another Sonar setting to look at is the one that defaults to Always Zero out continuous controllers when project play stops.  If a synth or preset for a synth, has volume or pitch tied to the modulation wheel, that could jazz up your track's volume even though you wouldn't see any recorded midi event data related to volume to account for such a loss of volume.
 
And, for my particular issues with some of the Komplete 8 Ultimate synths, either at the synth level, or in some cases at the individual loaded instrument level, there were option defaults I could change to sever its default of tying the synth/preset master volume to CC 11 changes.  THAT fixed a BUNCH of really weird volume changes for me.
 
Can you elaborate on what precise synths and presets you are having these issues with?
 
Bob Bone
 

It only happened once and it was with SI- strings. I'm not sure where to find the CC number of the message. All I got was a little line that just dropped out and took my volume with it. I have yet to be able to re create the event.  I did just have another crash though, couldn't find my last save, ( or the five before that, kinda weird. prolly a Windows issue. I'm running windows 7 pro 64. I did get a message from my sonar when I opened up and auto save (yes I do that because I forget) I had numerous messages citing audio files that had no sound, skipped em all and just re recorded the tracks. All the tracks in question were my analog tracks, all the MIDI stuff was there and in fine shape. But when I closed it out and went to save as a 'bundle' It tells me "Please delete events containing missing audio before attempting to save as a bundle" Not sure what that means. I didn't delete the tracks, just recorded over them. That's really a bugger cuz its a rather large project and I would really like to keep it as a bundle as it still needs some work and I'm a bit weary.
I did manage to install MidiOx as suggested but I really haven't a clue how the work it, I barely get myself around Sonar... sorry but it does seem that I got a lot of issues...

Here are a few things that you may or may not have considered.  If you are seeing automation nodes, I think #3 is likely, but these other things may happen at some point in your life.
 
1-You can have volume (Controller 7 or Controller 11) messages on another track that is set to the same MIDI channel.  This has hit me more than once.  You might try muting all the other suspect tracks and then un-muting them one by one to find the offender.  You can use Find/Change to change the MIDI channel for all events in a track.
2-I have had an issue with Kontakt (and at least one other soft synth) that is a bit hard to explain.  In the Kontakt interface, there is a gain (volume) slider.  You can slide it up to a higher value, but a Controller 7 message will reset it.  For example, you would think Controller 7=127 would turn ithe slider up all the way, but it doesn't.  If the default setting for the gain slider is 0 and you slide it up to +6 or +12, a Controller 7=127 will just set it back to zero.  A value of less than 127, of course, will turn it down even more.  I have had to strip all Controller 7 messages out of the track, move the slider, and save the instrument in Kontakt with the slider in a higher position.
3-If you accidentally move a fader on a MIDI track, you can introduce volume messages without meaning to.
4-There is always a change of SysEx messages in a track with a hardware synth, but you would have to do something to cause that, like pushing a panel button while recording.

Thanks Konrad. Points well taken.