1
general::
Phrase(s): to beat the band
very briskly; very fast. • He’s selling computers to beat the band since he started advertising. • She worked to beat the band to get ready for this.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, to beat all. To the greatest possible degree. For example, The baby was crying to beat the band, or The wind is blowing to beat the band, or John is dressed up to beat all. This idiom uses beat in the sense of "surpass." The first term may, according to one theory, allude to a desire to arrive before the musicians who led a parade, so as to see the entire event. Another theory holds that it means "make more noise than (and thereby beat) a loud band." [Colloquial; late 1800s]
American Heritage Idioms