I'm still a newbie to MIDI editing.  I'm composing in Sonar Professional, and editing in piano roll view.   I'm trying to create a decrescendo on a single MIDI note.  Lowering the volume of an entire single note is simple, of course.  But I'm trying, for example, to gradually decrease the volume of a single MIDI note that will be played by an oboe through two measures.  I'm assuming that it will require an automation envelope -- but I can't find anything in the manuals or forums that deals with this specific issue.   Thank you. 

There are a number of ways to deal with that.  IMO the Best way is to find a sample library that support crescendo and decrescendo articulations.  Manipulating track volume by any method will not replicate the "feel" of decrescendo.
 
That said,
 
Many MIDI instruments respond to MIDI volume automation.  On the MIDI track, click the automation lane and select it from the drop down.  If the instrument you are using does not support MIDI Volume, you can also automate the Track Volume in the same way.  There are lots of videos on Sonar Automation that you can watch to show you where the controls are.

My sample libraries don't seem to have that feature. 
I have to add Volume automation to the track.  It's not exactly the same as if the oboe player decayed the note, but close.

One trick I learned a long time ago to help it sound better ..
 
In addition to volume automation, add a room reverb and automate the mix from zero to 35%ish mix at the end.  It's hard to say exactly because samples are so different in ambient content.  But, you never want to reverb to dominate or be obvious, but a subtly used gradually added reverb will help diffuse the sound, so that it sounds more like a decrescendo ...  if you mess around a bit, I think you'll see what I mean.

Good idea!
 

just for clarity, you are still reducing the volume via automation as well.  But, as the volume drops the reverb is increasing.  If you have a verb with an EQ you can also use that to thin out the sound as quiet sounds have a natural upper mid dominant curve.

just curious, which oboe library and what sampler are you using?
 

jmcecil
There are a number of ways to deal with that.  IMO the Best way is to find a sample library that support crescendo and decrescendo articulations.  Manipulating track volume by any method will not replicate the "feel" of decrescendo.
 

The OP said one note, so how can you do multi crescendo/decrescendo using multiple samples on one note ?
I am aware that some VST-I's will include crescendo/decrescendo samples. but on a midi note. im curious how that's done.
 
Personally I use automation or freeze the data and make a fade.
 

chuckebaby

jmcecil
There are a number of ways to deal with that.  IMO the Best way is to find a sample library that support crescendo and decrescendo articulations.  Manipulating track volume by any method will not replicate the "feel" of decrescendo.

The OP said one note, so how can you do multi crescendo/decrescendo using multiple samples on one note ?

I have a lot of libraries where a decrescendo or crescendo is a single note hit, and they have articulations of varying length of crescendo and decrescendo so you can pick the closest one and timestretch it to the project tempo.  So, one note = 8 second crescendo or decrescendo for example.

jmcecil

chuckebaby

jmcecil
There are a number of ways to deal with that.  IMO the Best way is to find a sample library that support crescendo and decrescendo articulations.  Manipulating track volume by any method will not replicate the "feel" of decrescendo.

The OP said one note, so how can you do multi crescendo/decrescendo using multiple samples on one note ?

I have a lot of libraries where a decrescendo or crescendo is a single note hit, and they have articulations of varying length of crescendo and decrescendo so you can pick the closest one and timestretch it to the project tempo.  So, one note = 8 second crescendo or decrescendo for example.

Thanks for the explanation.
I have found the decrescendo to be the easiest because more often than not the samples fade as the duration travels, thus creating a volume envelope along with the diminishing note volume passes as a pretty good fake.
the crescendo on the other hand isn't as easy to fake using volume automation or a fade.
I have in the past used the reverse technique but it still doesn't quite sound real.