How does one effect a t'rua when blowing a shofar on Rosh Hashana? The airflow must be stopped and started repeatedly in a short time, but it can, I suppose, be stopped either
- at the glottis,
- at the narrow end of the shofar (by blocking it with the tongue), or
- anywhere in between (say, by effecting a velar stop)
— or, indeed, not by blocking the flow of air but simply
- by repeatedly pausing exhalation with the diaphragm.
Is/are any of these mandated/barred by halacha? Which is/are commonly used or not used, and why?