wp get post if a custom field has value

am using WCK plugin for Custom Post Types and Fields

Its seems nice and i have done my work fine

One of my Custom Types has a custom field for upload an mp3 file

And now i want to get all the custom posts that have value for this mp3 field.

In other situations for example get all post that have thumbnail i use

'meta_key' => '_thumbnail_id'

Is there any similar approach to get the custom posts that have the mp3 field set.

Thanks

via Chebli Mohamed