Step Across the Border is more than a just a soundtrack. It includes additional tracks, for example, "Drum Factory" and "Candy Machine", that were written for the album by Frith from ambient sounds in the film. Discussing the album, Frith said:
It struck me as not very interesting just to take what was exactly in the film and stick it on a CD and put it out as a soundtrack. Apart from anything else, the function, when you listen with the image and when you listen without the image, is very, very different.
One of the things I particularly enjoyed doing was taking raw sound from locations during the film, like the candy machine, and writing pieces of music to go with them, which is totally unnecessary within the context of the film, because they have their own logic ... In the film, the candy machine is there, and you hear the noise it makes but the image was so strong that there was no need to do anything with it. On the record there was no point of sticking the sound of a machine on there, because it wouldn't mean very much.
The album also includes live music as performed in the film, for example "Houston St"; tracks from other albums that accompany scenes in the film, for example "Too Much Too Little"; and tracks from other albums that replace live covers of those tracks performed in the film, for example "Legs".