The Toke’a (person who blows the Shofar in the synagogue) must be familiar with the detailed laws of how the sounds of the Shofar must be blown. It is not enough for him to train so he can produce a strong sound; he must also study the relevant Halachot so he blows all the sounds properly.
One of the relevant Halachot pertains to the sounding of the Shebarim, which consists of three blasts. Halacha requires the Toke’a to blow the three blasts in one breath; this requirement is codified in the Shulhan Aruch (Orah Haim 590:4). If the Toke’a took a breath in between the blasts of the Shebarim, the Misva has not been fulfilled, and the Shebarim must be blown again. However, although the three blasts must be sounded in a single breath, they must nevertheless be three distinct, disjointed sounds, and not contiguous. There must be a brief silence between the sounds so they are separate, even though they are done in a single breath.
There is a debate among the Rishonim (Medieval Halachic scholars) as to whether the Toke’a should take a breath in between the Shebarim and Teru’a when blowing the Shebarim-Teru’a sound. Our custom is to satisfy both views by having the Toke’a blow the Shebarim-Teru’a in one breath during the first thirty Shofar sounds blown before Musaf, and to blow them in two separate breaths when blowing the other Shofar sounds. This is why in our Mahzorim a line is added in between the words "Shebarim" and "Teru’a" for the Shebarim-Teru’a sounds before Musaf, indicating that they should be blown in a single breath. It must be emphasized that even when blowing the Shebarim-Teru’a in a single breath during the first set of Shofar blasts, the Toke’a must make a slight pause between the Shebarim and the Teru’a, so they are clearly separated.
The Arizal (Rabbi Yishak Luria of Safed, 1534-1572), as cited in Sha’ar Hakavanot, taught that the different sets of Shofar sounds serve to negate different categories of sin. The Shofar sounds blown before Musaf serve to negate the Yeser Ha’ra (evil inclination) for idolatry, whereas the sounds blown during the silent Amida of Musaf negate the Yeser Ha’ra of Arayot (immorality). The Shofar blowing during the Hazan’s repetition of the Amida relate to the sin of murder, and the sounds blown during Kaddish Titkabal at the end of Musaf serve to negate the Yeser Ha’ra of Lashon Ha’ra (negative speech about other people). It is therefore appropriate to have thoughts of Teshuba for sins involving the appropriate category during each series of Shofar blasts.
Summary: The Shebarim must be blown in a single breath, but as three separate sounds. The Shebarim-Teru’a is blown in a single breath during the Shofar blowing before Musaf, but in two separate breaths during the rest of the Teki’ot. During the first thirty sounds, one should have thoughts of repentance for sins involving idolatry; during the sounds blown in the silent Amida, one should repent in his mind for sins of immorality; during the blowing in the Hazan’s repetition, one should repent for sins related to murder; and during the final blasts blown in Kaddish, one should repent for Lashon Ha’ra.
