The phrase "as the opening notes" is correct and usable in written English.
It can be used to describe the initial sounds or music that set the tone for a piece, often in a musical or literary context.
Example: "As the opening notes of the symphony filled the hall, the audience fell silent in anticipation."
Alternatives: "at the beginning of the melody" or "during the initial chords".
As the opening notes began to play, I grabbed the mouse and fast-forwarded past the song.
Cocker, resplendent in suit and tie announced, 'Tonight we are going to make history.' As the opening notes of Do You Remember The First Time? began and a singalong broke out, it really felt like they might.
But it comes together as perfectly natural as the opening notes from the piano and violin that kick off "Homecoming Heroes," the lovely first track.
"I mean, don't you wish she had just dropped a visual album on you instead?" Pat scoffs as the opening notes of Lemonade drift down from the screen.
As we were crushed in the back of the room by the sweaty, suffocating crowd, the arm of some horrified Hessian pressed in front of me inexplicably went right up in flames as the opening notes of "South Of Heaven" seeped out of the speakers, which is a song about the exact opposite of the saccharine drudgery that is the Christmas season.
To the Japanese, the reference is as familiar and evocative as, say, the opening notes of Aaron Copland's "Appalachian Spring" may be to Americans.
As soon as they hear the opening notes of a model opera, they remember everything bad that happened, and their hearts start to beat faster.
Instead, as we approach the opening notes of the conference, the mood contains more than a whisper of hope.
But as soon as the orchestra struck up the opening notes of the overture, a medley of some of Garland's signature songs, the audience became both more relaxed and more excited.
A sharp-shouldered dancer poised for her first move as the orchestra plays the opening notes.
If you are bold enough to select what is known in the cell phone business as a "ring melody" -- the opening notes of "Fur Elise" or Pachelbel's "Canon in D Major," for instance, brace yourself for a little snickering from fellow commuters or neighbors in Starbucks.
