What is an octave?

The word "octave" is related to "octopus", "octagon", etc -- in other words, eight. In music, an octave is 8 diatonic scale notes  higher or lower than  the note of the same name.

For example, the "A" note is always 8 notes higher or lower than the previous "A". The "A" above middle C vibrates 440 times per second, so the "A" an octave above it would vibrate 880 times per second, while the "A" below middle C would vibrate 220 times per second, and so on.

The human ear identifies these octave notes as being "the same" -- only higher or lower, so if a soprano sang A440 and a bass sang A110, the human ear would hear it as the same note -- just separated by pitch. That's why there are only 7 distinct diatonic pitches and only 12 distinct chromatic pitches, despite the fact that the piano keyboard has 88 keys. Each note is repeated over and over again, but at a higher or lower octave.

What is an octave?

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How To Hear Differences in Chord Types

Each type of chord gives off a mood of its own. By associating the mood, or emotion, with a specific chord type, you can soon learn to distinguish between the basic kinds of triads:

Major

Minor

Diminished

Augmented

For example, minor chords sound more somber, more serious, than major chords. Why? Because of the way the intervals are "stacked" within the chord. A diminished chord sounds suspenseful, tense, nervous. An augmented chord has a distinctive sound, too. Learn how to hear, feel, and identify these chords, as well as extended chords (you'll learn how to listen for the "color tone" in any 4-note chord).

Here are the color tones we'll listen for:

6ths
7ths
9ths

Once you can identify the 4 types of triads, and then recognize the color tones, it is a short step to recognizing chords such as minor 7ths, minor 6ths, diminished 7ths, major 9ths, and so on.

http://www.playpianocatalog.com/ear-training-chords--how-to-hear-differences-in-chord-types.html

Playing "Auld Lang Syne" Using 3 Chords Or Many Chords

Arranging "Hark, The Herald Angels" for Piano

"Hark The Herald Angels Sing"

"The First Noel" Using a Simple Scale & a Counter Melody

The First Noel The Angels Did Say

It Came Upon a Midnight Clear

Rubato vs Steady Time from chordman on Vimeo.

Another Christmas Carol arranged for piano using chords

Angels From The Realms of Glory using 2/1 ratio of chords

Playing "Angels We Have Heard On High" on the piano

There are many ways to arrange any tune. Here is one "classical sounding" piano style you can use:

 "Angels We Have Heard On High"

Arranging "O Come All Ye Faithful" on the Piano

Musical passing tones and ostinato in "O Come All Ye Faithful"