Otherwise known as Yoga Nidra with Ajapa Japa
Extracts from http://www.yogamag.net/archives/2005/dapr05/orjap.shtml
The sadhana of ajapa japa is as old as the Upanishads. In some of the Yoga Upanishads such as Yogashiksha, you will find certain passages and stanzas which declare that the breath goes in with the sound of So and comes out with the sound of Ham. This is the ajapa gayatri which the jiva continuously repeats.
Ajapa japa is a complete sadhana and through it one can have direct experience of samadhi. In order to attain samadhi, in all the other yogic practices one has to have complete control over the breath, the reason being that in samadhi the breath is suspended and kumbhaka takes place spontaneously. However, in the practice of ajapa japa, due to the continuity of breath and mantra, the breathing remains normal throughout, and even in samadhi there is no change.
Apart from samadhi, there are certain practices in yoga where one becomes introvert and at that time there is automatic suspension of the breath. The difficulty is that the aspirant becomes extrovert after a short meditation if the lung capacity is not adequate. Many sadhakas have this difficulty. In the practice of ajapa japa, however, this problem is solved.
The quality of the audio recording is not brilliant, so if you wish to listen to it, do so at a low volume on your device, but loud enough so that you can still hear. I am still working on recording and editing audio to sound better. An ongoing process.
OM TAT SAT.