As far as hearing melody is concerned I see that skill as being more or
less ubiquitous in human communities.
Almost everybody can sing Happy Birthday or several other "nursery
rhymes" we, in the West for example, are exposed to as children w/o any
musical training.
Ditto for the melodies of popular songs we hear on the radio or elsewhere.
Although when I was very young I did have some training with the Orff
Method and my father was a good singer who taught me a few chords on his
baritone uke, most of my own ability to hear melody simply comes from
singing popular tunes as a kid.
The most basic skill involved here is the recognition that one note is
higher (or lower) than another note.
Then you learn to discern how much higher or lower.
And if you can sing a melody and hold each note clearly in your mind you
can always figure out how to play those notes on a guitar (as long as
someone you know knows how to tune up the guitar for you) or another
instrument.
At that point it's simply a matter of trial and error.
Sing the first note of the melody and then find that note along one of
the guitar's 6 strings.
The next note in the melody will probably be available on that same string.
Sing that note and look for it *1 fret at a time* along that same string
until you find it.
Don't leap around the string hoping you'll find the note intuitively.
Do it *1 fret at a time* eliminating all the wrong notes as you proceed.
If you find that this note exceeds the range of that string then you'll
have to start looking for it on the next highest or lowest string.
Proceed like this until you know what all of the notes of your melody are.
At this point don't even worry if you have a decent usable fingering for
your melody.
Your ability to finger things effectively will improve with more skill
on the instrument and with more familiarity with the phrasing elements
of your melody.
So the ability to hear a melody is something quite different than the
ability to play that melody on an instrument.
For people for whom the former is impossible to learn to do, the latter
will always be beyond them as well.
If and when I encounter a student who simply can't sing an easy melody I
never know what to tell them.
There are remedial ear training courses out there but I don't know how
effective they would be with an adult student.
These skills do seem to be tied up with exposure to music and music
making as a child.
If you treat the heads of your jazz tunes, even complex bebop heads, the
same way (i.e. as melodies that you can sing) then eventually those
sounds will be available to you as an improviser as sounds that you can
hear.
As a matter of fact, I'm going to go out on a limb here and say that I
think you can learn almost as much "vocabulary" by working on
pre-composed classic bebop heads as you can from lifting solos.
But only if you pay attention and learn to hear those heads.
Each bebop head is a dense little study in melody and ornamentation.
These melodies have a lot more jazz "vocabulary" built right into them
than an American Songbook standard.
The same approach and attitude should be taken when working on a
transcription of somebody's jazz solo that you're interested in.
I.e. Don't just learn to read/play it.
Learn to sing it too.
Analyze the melodic/rhythmic devices that are being employed and learn
to create your own lines using those same or similar devices.
Etc., etc.
I also firmly believe that it's by singing what you practice that you
learn to hear what it is you are practicing.
And even if you don't sing out loud you should always be playing *as if*
you're singing if you want to be honest about playing what you hear.
I don't think anybody learns to hear chord voicings via such an
intuitive process though.
The ability to hear chords really seems like it's more based on
accumulated musical experience playing an instrument than it is on
simple environmental exposure to music.
But the outlines of chordal hearing and melodic hearing are really based
on the same skill set.
It's only experience and repeated trial an error that will get you to
the point of being able to hear, in very broad strokes, the difference
between major, minor, augmented and diminished triads.
In order to learn to hear and recognize these triads a musician will
have to spend lots of time playing them, sometimes arpeggiated, and
comparing them until they get a general sense of the texture of each sound.
Ditto for the basic 7th chord types.
As far as lifting exact chord voicings is concerned, you can go really
far by just figuring out the top and bottom notes of each voicing first.
The outer notes are always the most exposed and the easiest to hear and
should be thought of as melodies in their own right.
The top note of a voicing will always be heard as some sort of a melody
or counter-melody.
And if the chordal player is sophisticated enough, his top notes should
be just as singable as any other melody.
Bass lines are mostly comprised of progressions of chordal roots with
occasional inversions and/or passing tones.
If you learn to sing the bass-lines of the tunes you're working on, just
like you can sing the melody, it will help your ability to memorize the
chords and your ability to hear other bass-lines for other tunes that
are similar yet deviate somewhat form the bass-lines you are already
familiar with.
Since most music based on the maj/min key system uses familiar chains of
root progressions in piece after piece there really isn't as much skill
involved in developing the ability to hear bass lines as you might imagine.
Learn the main progressions first:
I IV V (Im IVm V)
I VIm IIm V
IIIm VIm IIm V
I IV IIIm VIm IIm V
Etc., etc.
The more prior kill you already have in constructing decent bass lines
will help greatly in hearing other people's bass lines on recordings.
To me, ear training is really just musical experience.
Once you know the top and bottom notes of a chord voicing, figuring out
the rest of the voicing can either be an intuitive "ah ha" process where
you just recognize a chord quality that you're already familiar with or
a process involving more thought and logic based on your knowledge of
the probable voicings that are commonly used.
The latter implies that some sort of a harmony course has already been
completed by the student and that he/she has familiarized themselves
with the basic ways that musicians use to voice chords.
So, if the top note of a chord is Eb and the bottom note is C there's a
good chance that the chord will sound like some sort of a root position
voicing of Cm.
If you already recognize the chord quality as being minor then you're
almost done.
You can confirm that it is a Cm chord by playing a Cm chord on your
guitar and comparing its sound to the sound of the chord on the recording.
If it is Cm then any other notes in the voicing are likely to be Gs or
Bbs (possibly Bs or As) and maybe a D or an F thrown in for colour.
As your experience grows you'll be able make those distinctions with
greater and greater accuracy and speed.
If you play your Cm chord on the guitar and it sounds too dissimilar to
the chord on the recording, then you might have to do a bit more thinking.
And that thinking will be based on your knowledge of the typical
harmonic possibilities of chords that have Eb on top and C on the bottom.
E.g. If it's not a Cm chord it has to be some other chord on which those
same two notes happen to fit.
If it's not a Cm chord, then C isn't the root.
If C isn't the root then it must be the 3rd, 5th, 7th, 9th 11th or 13th
of some other chord.
Usually it will be the 3rd, 5th or 7th.
To test whether it's the 3rd try playing an Ab chord or an Am chord and
compare it to the recording.
Etc., etc.
At least that's the way it works for me.