This is a quote from Trumpet Secrets Volume 1 by Jerome Callet and Bahb Civiletti. Sadly this book is now out of print but luckily I have it!
If the player tries to play with the clearest, most compact and brilliant sound, the player will produce overtones that will project the tone in the largest concert halls. Most trumpeters and trombonists are trying to develop a tone that is not truly characteristic of these instruments. The incorrect tonal abuse causes it to spread the tone too wide. When you play this way, with a “spread” tone, you cannot produce purity of sound for which your instrument was built, and you will always force your tone and over-blow.
Open your ears to the true trumpet sound.
A great quote from the writings of Herbert L. Clarke. It is amazing how much of what he says applies to learners today:
In my practice I kept to the elementary, although I could play a lot of tunes when I first started and this even before a perfect scale was played – that is, played without making a mistake of any kind. How often do we think that our work is satisfactory when, after all, we merely blow into the cornet and make a noise without being perfect in every detail! One hundred percent alone is perfection. Ninety-nine percent only proves that one percent is missing in perfection, thus making the whole imperfect by just one per cent; therefore, when in his practice a player does not correct the slightest mistake immediately he logically is practicing to be imperfect.
I have heard many pupils play page after page of the instruction book, missing the notes here and there and making all manner of mistakes without correcting them, then say: – “well I played fifteen pages of exercises today.” There was no realization that even if only one mistake was made they had not played the fifteen pages, but simply “played at them.”