Yogananda brought “original yoga” to the West, as he explained. Indeed, all his techniques are ancient and have been practiced by countless yogis throughout the ages: Kriya Yoga has been taught for millennia, as have been Hong-Sau and the AUM technique. The Energization Exercises are his personal creation, but the principle behind it (sending energy to body parts) is as old as yoga itself, being called prana-dharana in yogic tradition.
Yogananda’s chanting method –loud, whisper, mental– is also rooted in ancient yoga, and is well-known in the teachings of mantra yoga.
In the Scriptures, these three stages have names:
1) Audible chanting is called bakhari japa (also called ucca or vachika)
2) Whispered chanting is called upamshu japa.
3) Mental chanting is called manasik japa (also called manasa).
For example the Tantra Sara, written around 1000AD, attributed to Abhinavagupta, teaches these three stages of chanting.
According to the Yoga-Yajnavalya (2.15f), whispered recitation is a thousand times better than voiced japa, while mental recitation is a thousand times better than whispered japa.
The Kularnava Tantra similarly states: “Silent japa with complete enunciation of words is regarded as the best.”
Yogananda would completely agree, as he says: “There are several forms of chanting: loud chanting, medium chanting, whispered chanting is very much softer, and mental chanting is greater still…. How many people say, AUM, AUM, AUM. That is loud chanting. Then there is whispered chanting and mental chanting, and when you are actually listening to the sound that is going on, that is superconscious chanting.”