Sentence No 1. "The low note was a grunting, a rumble, the deep discordant growling of an ill-conditioned dog." Assuming that nobody would want to be compared to an ill-conditioned dog, this sentence expresses mockery. The term "discordant" itself means inharmonious and off-key. Good music is universally known to be harmonious and pleasing to the ears. Sentence No. 2 "Then suddenly the singer threw up his face, straightened his tubby figure, rose upon his tiptoes, and with a wagging head and scarlet cheeks emitted such a howl as the same dog might have given had his growl been checked by a kick from his master." The first part of the sentence doesn't express too much mockery, just a frank description, but the second part of the sentence starting from "emitted such a howl" expresses mockery. In this description, the subject's voice is being compared to a pained animal. "A kick from his master" is known to be a universal punishment for dogs (unless the dog enjoys being kicked which is very, very, unlikely). Unless the goal of the subject is to sound like a punished animal, this is not a compliment. A good voice is pleasing to the ear while a howl, consequence of pain, will be loud, shrill, and abrupt. Sentence No. 3 "Many a singer far better than this absurd fop had been driven amid execration and abuse from the platform." The narrator in this sentence is being quite straightforward about his opinion on the subject by declaring him an "absurd fop". Absurd means unusual or inappropriate, so if something is called "absurd" it's in a negative way.
