For a nine-month-old, **your own singing is an excellent place to start**. Try a familiar song while he watches your face, add simple hand movements, and pause to let him babble back. ZERO TO THREE recommends singing, movement, and these back-and-forth musical exchanges for babies. [Getting in Tune](https://www.zerotothree.org/wp-content/uploads/2022/05/Getting-in-Tune-English.pdf)

Your criteria are useful for choosing calming music. For playtime, a lively beat and some changes in expression can also be enjoyable. The key is how your son responds.

A few practical criteria:

- **Comfortable volume.** Start quietly, with the speaker away from his head. You should easily hear each other over the music. Hearing risk depends on loudness and duration; a recording with little variation can still be too loud. [NIDCD hearing guidance](https://www.nidcd.nih.gov/health/how-loud-too-loud)
- **Repetition.** Familiar melodies, repeated verses, and a clear beat give him patterns to recognize. Repeating a favourite song is useful; you do not need a constantly changing playlist. [ZERO TO THREE’s music guidance](https://www.zerotothree.org/resource/distillation/beyond-twinkle-twinkle-using-music-with-infants-and-toddlers/)
- **Opportunities to join in.** Choose songs you can sing, clap, or gently sway to together. As he becomes a toddler, action songs offer more ways to participate.
- **A match for the moment.** Try gentle singing for settling down and more rhythmic music for active play.
- **His response.** Watch for interest, smiles, or movement. Turning away or becoming upset is a cue to pause or change the activity. Include quiet periods too. [Getting in Tune](https://www.zerotothree.org/wp-content/uploads/2022/05/Getting-in-Tune-English.pdf)

These are reasonable starting choices, selected for their musical character—not a scientifically established infant playlist:

| Music | Why try it? |
|---|---|
| **“Twinkle, Twinkle, Little Star”** or **“Row, Row, Row Your Boat”**, sung by you | Short, repetitive melodies; easy to sing gently |
| **“Itsy Bitsy Spider”** or **“The Wheels on the Bus”** | Repeated phrases and accompanying gestures |
| **Brahms: “Wiegenlied,” Op. 49 No. 4** | A familiar lullaby; try singing it or a gentle recording |
| **Bach: Prelude in C major, BWV 846** | A flowing, repeated keyboard pattern |
| **Satie: Gymnopédie No. 1** | Slow pace and a relatively sparse piano texture |
| **Acoustic folk songs or gentle jazz** | Alternatives with voices, clear melodies, or a steady pulse |

Preview the **particular recording**: arrangements and performances can change the volume and character considerably. Classical music is one option; family songs and music you enjoy are also worth exploring.

For your son, I would begin with a few minutes of singing and gestures, then try one short recording together. Repeat whatever he seems to enjoy. That gives you a useful selection method: his interest, at a comfortable volume.