When the breath comes in with the sound ham and merges inside, there is a fraction of a moment which is completely free of thought. This is the madhyadasha, the space between the breaths. This is where you have to focus in meditation. To focus on that space is the highest meditation and the highest knowledge. That space between the breaths, that space where no thoughts exist, is the true goal of the mantra. It is a miraculous space. It is aham vimarsha, the inner pulsation of consciousness. It is from this space that all worlds rise and subside. It is this space without form which pulls apana inside and which pushes prana out. This space where ham merges inside, before sa has risen, is the space of God, of supreme Consciousness, of the self. The place where sa merges outside is equally the place of God. So realise that moment of the merging of the two syllables. If you come to know that moment, if you become established in it, you experience truth.
This is hamsa vidya, the science of Hamsa. Not only is it a natural mantra repetition, it is natural pranayama.