I recently watched footage of Shorin-ryu masters in Okinawa teaching how they breath during kata. What they highlighted also made me recall past teachings I had also seen of Inoue Yoshimi Sensei, 8th Dan Shito-ryu.  Their practice involves silent breathing and not making loud or audible exhalations for techniques.  Its called, 'shizen-kokyu' (breathing naturally) and the Shorin-ryu master's reasoning was so that you do not telegraph your rhythm to your opponent, for example in sparring.  On the other hand, Inoue Sensei's explanation was that loud exhalation causes unnecessary tensing of the core.  In contrast to this, for Rick Hotton Sensei (5th Dan, WWD), his audible exhalation of breath is natural for him and helps to release the power of his techniques, so rather than tension, it is a 'release'.  Telegraphing your rhythm does not really have as much relevance from a self-defence perspective.  Also, the princle of exhalation is that its meant to go hand in hand with the 'relaxed heaviness' that you need when hitting techniques with efficient transfer of power.  You definitely should not be holding your breath or be breathing in when you strike as that would be tense or weak.  Exhaling silently will entail only a small limited amount of breath being expelled relatively slowly, as a larger amount at speed would inevitably be audible.  As long as you are breathing correctly and naturally to release the power of the technique, how audible the sound of the exhalation ends up being would seem irrelevant for its purpose and there should not be an artificial pre-occupation to make it sound a particular way or indeed to suppress it either.

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