Dolby Atmos is a rendering format, so source material could be any audio that you have available. 

Source material examples:

• If you are a songwriter and are looking to start writing music that will be consumed in Dolby Atmos, your source material can include any instrument, sample library, virtual instrument, and so on.

• If you are a recording engineer, you might have stems that have been previously defined by a writer, or tracks captured live in studio, or a multitude of other formats that can be used to create a Dolby Atmos soundfield.

• If you deal with older recordings, you might have to work with anything from a mono tape to a 48-track tape, or another digital format. All can and have been used to create a Dolby Atmos soundfield. One method to do this is to reamp those sources into a studio environment and capturing the output in the room. Another method is to separate sources out from the available tracks and reposition them in the soundfield; there is a variety of other source extraction methods, as well.

However, once you get to the mixing stage of your Dolby Atmos project, the choices you have are the same: 

• Does this sound work best as part of a bed or as an object?

• If I apply temporal effects to this sound source, should they follow with the object or exist in the bed? 
 

The fundamental principal is that if it sounds right, then it is right. Generally speaking, the greater variety of source material and the more atomic and separated it is, the more options and flexibility you will have when creating a Dolby Atmos mix. As an example, if all of the drums and percussion instruments in your project are mixed into a single stem, you will only be able to create a single object or bed, which limits your creative choices for positioning in relation to your listener. If you had individual tracks for kick, snare, hi-hat, chimes, cowbell, and so on, you could potentially position them in disparate parts of the room to create a sense of space.

Following are more suggestions on preparing source content for Dolby Atmos mixing:

• Using mono stems, rather than stereo stems, will allow for more control of object position.

• Consider printing out a wide variety of tracks (with and without effects, mono, stereo, bused, and so on) and experimenting in your mix:

 • Printing effects separately from the dry sound can allow you to place the dry source in a different position from the effects, and also allow you to apply different binaural render mode settings for the dry source and effects. This can be especially effective when working with vocals.

• If only stereo stems or stems with effects included are available, consider using mid-side processing and positioning the mid and side separately.

• The binaural render mode settings apply a distance model to the objects for which they are selected. You may want to try these with source content free from other spatial effects (such as reverb) to see how the settings change an object's sound.

• The Renderer works at 48 and 96 kHz. Using source material with sample rates at least this high will yield better results than material that is upsampled.