The CDs are selling faster than nappies

That is until she puts on the super-lullaby CD.

"I put on this CD and he falls straight to sleep. This really is a godsend," Ms Sakurai said.

Sounds were recorded inside the womb using a tiny microphone near the baby's ears to pick up what it was hearing.

The muffled sounds were then mixed in a recording studio with musical instruments to create the ultimate lullaby.

CD producer Junichi Kamiyama has recorded over 40 instruments as they sound in the womb and mixed them with the natural sounds of the mother's body.

Junichi Kamiyama: "I've made it sound just like the womb."

"I just hope when babies listen to this, they relax and feel like they're back in the womb, because I've made it sound just like the womb," he said.

There are now dozens of versions on the Japanese market. The latest is simply called See! Baby's Stopped Crying.

Desperate parents are buying them up quicker than nappies.

Although there is no scientific evidence that it works, for Naoya's mother, the silence is proof enough.