Our Baal Tokeai did not make a really noticeable break between the Shevarim and Terua in the set of Tashrat, in the blowing that follows the reading of the Torah? Were these blows valid? To note, he claims that he did make a very slight break which perhaps us listeners did not pick up being that we are used to a larger break.
The blows are valid even if a very short break was made, so long as the sounds of the Shevarim and Terua were noticeable as two separate distinct sounds. Furthermore, even if no break at all was made, it remains valid according to many Poskim, and some rule that so should be done even initially, and so is the initial custom of some communities.
Explanation: There is a dispute amongst the Rishonim and Poskim regarding whether the Shevarim and Terua of the set of Tashrat should be sounded in one breath or with a breath in-between, and practically, we rule that in the blows which follow the Torah reading it is to be blown in one breath. Now, some Rishonim rule based on the Talmud that although it is blown in a single breath nonetheless a slight break is to be made between the two sounds, and so is ruling of many of the Achronim, including the Alter Rebbe. It is not necessary however to make a large break, and on the contrary even a slight break suffices, as the entire purpose of this break is simply to make sure that the two sounds are separated, and that the second sound does not sound like a continuation of the first. Now, if this break was not made and the second sound, sounds like a continuation of the first sound, then it is not clear [and neither have I found this law recorded anywhere] what the rule would be Bedieved according to these Poskim. [One cannot compare this to the implied law of invalidation of one who blew an entire set of blows without a breath in between and also without a break between, as in truth those are meant to be different sounds, while the Shevarim Terua according to this opinion is a single sound. Vetzaruch Iyun] However, some Rishonim and Poskim completely disagree with the above and rule that the two sounds of Shevarim Terua should be blown in a single sound without any break at all in between. Thus, while certainly one should initially make a slight break in between as rules the Alter Rebbe, seemingly there is no need to repeat the sound Bedieved. This especially applies on the second day which is only rabbinical, and especially according to those who were accustomed to make a short Tekia sound at the end of the Shevarim which itself can serve as a break between the Shevarim and Terua.
Sources: Nitei Gavriel 58:5; Piskeiy Teshuvos 590:7; See the following sources who require one to make a break between the Shevarim and Terua: Admur 590:9; Terumas Hadeshen 142; Beis Yosef 590; Rashi Chulin 26b; P”M 590 A”A 4; Mateh Efraim 590:15; Ashel Avraham Butchach 590:4; M”B 590:18; Kaf Hachaim 590:32; See the following sources who do not require one to make a break between the Shevarim and Terua and on the contrary should be blown in a single sound without a break: Rosh [if make break is invalid]; Avnei Nezer 443:5; 444:20; Eish Das p. 25; Chazon Ish 136:1