There is a Misvat Aseh (affirmative command) from the Torah to hear the sounding of the Shofar on Rosh Hashanah. In order to fulfill this Misva, one must pay close attention to the sounds of the Shofar. Unfortunately, it often happens that people’s minds wander during the Shofar blowing, and they do not concentrate on the sounds. The best way to prevent distraction is to follow along the Shofar blowing with one’s finger inside the Mahzor, pointing to each sound of the Shofar (Teki’a, Shebarim, Teru’a, etc.) as it is blown. This practice is mentioned in the work Yesod Ve’shoresh Ha’aboda, and it is a worthwhile practice to follow.
The minimum required length of a Teki’a is the length of nine Teru’a sounds. The Gemara says that a Teru’a must consist of at least nine "Turmutin," or quick breaths, and so a Teki’a must be at least the time it takes to blow nine "Turmutin." However, this applies only to the Teki’ot sounded before and after the Teru’a. The Teki’ot blown before and after the Shebarim-Teru’a sound must at least the length of a Shebarim-Teru’a. Each sound of the Shebarim is the length of three Teru’ot, and thus the entire Shebarim must be at least the minimum length of the Teru’a – nine short Teru’a sounds (3 * 3). It emerges, then, that the Shebarim-Teru’a must be double the minimum length of a Teru’a, and the Teki’ot sounded before and after the Shebarim-Teru’a must also be this length.
There is a difference among different Jewish communities regarding the precise nature of the Teru’a sound. Ashkenazim, Yemenites, and Syrian Jews have different traditions regarding how the Teru’a should sound. (Listen to the audio recording to hear the different sounds.) These customs are all based on tradition, and each community should therefore follow its time-honored custom.
There is also a debate among the Halachic authorities as to whether the Shebarim-Teru’a should be sounded all in a single breath, or in two breaths (one breath for the Shebarim, and another for the Teru’a). The common practice is to satisfy both opinions, by blowing the Shebarim-Teru’a in a single breath during the first set of Shofar blasts (the Teki’ot Di’myushab) and in two separate breaths during the second set of Shofar blasts (the Teki’ot De’me’umad).
The one who sounds the Shofar must be aware of all these issues. He must know the minimum length of the Teki’a sound – which depends on whether it is associated with a Shebarim, Teru’a, or a Shebarim-Teru’a – as well as the precise nature of the Teru’a sound according to his community’s custom. Additionally, he must remember to sound the Shebarim-Teru’a in a single breath during the first series of Shofar blasts, and in two breaths during the second series.