Baby movement

So I've always heard that babies tend to be more active at night. This was true for me for a little while then I started listening to relaxing sounds before bed and throughout the night. I've been doing this for about a month now and I've noticed that my son has slowly decreased his movement once I start playing the sounds. Now it's to the point where he doesn't move at all (none that I'm awake for and able to feel) from the time I start to relax with the sounds until I wake. He's active throughout the day but it's like he goes to sleep with me...has anyone else experienced this?