Sourdine literally translates to "mute" or "muted" (as in a musical mute). It's an interesting word because it's not commonly used in everyday conversation, especially in a romantic context.
In this song, Céline Dion sings, "je mets la musique en sourdine, tout bas" (I put the music on mute, very low). She's so anxious and focused on hearing her beloved's footsteps that she mutes the music, creating a vivid image of anticipation and longing. This unique usage makes it a memorable and evocative word.
Have you ever waited for someone so much that your whole world revolves around them, even before you've met them? That's exactly what Céline Dion sings about in "En Attendant Ses Pas" (While Waiting For His Steps). It's a beautiful song about the anticipation of meeting a future love, someone who hasn't arrived yet but is constantly on her mind.
She's doing everything to prepare for his arrival, like putting the music on low in case he rings: "je mets la musique en sourdine, tout bas / Trop bête, on ne sait pas, s'il sonnait / Si je n'entendais pas cette fois" (I turn the music down low, very quietly / Too silly, we don't know, if he rang / If I didn't hear this time). She's even taking care of herself, putting on lipstick and blush "Pour qu'il ne voit pas / Quand trop pâle parfois, ne surtout pas / Qu'il me surprenne comme ça" (So he doesn't see / When too pale sometimes, definitely not / That he surprises me like that). She doesn't even know if he's blond or brunette, tall or not, but she's sure that when she hears his voice, she'll know "Que tous ses mots, tous seront pour moi" (That all his words, all will be for me). It's a really sweet and hopeful song about dreaming of that special person.