Carl Philip Emanuel Bach recalled his father’s (Johann Sebastian) talents as a musician:
The exact tuning of his own instruments, and of the whole orchestra, had his greatest attention. No one could tune and quill his instruments to his satisfaction; he did it all himself. The positioning of an orchestra he understood perfectly. He made good use of any space. He grasped at first glance any peculiarity of a room. A remarkable illustration of this follows:
He came to Berlin to visit me; I showed him the new opera house. He saw at once its virtues and defects, with regard to the sound of music in it. I showed him the great dining hall; we climbed up to the gallery that runs round the upper part of the hall. He looked at the ceiling, and without further investigation stated that the architect had unintentionally accomplished a remarkable feat, without anyone realising. If someone went to one corner of the rectangular hall and whispered very softly upwards against the wall, somebody standing in the diagonally opposite corner, with his face to the wall, would hear what was said quite clearly, while between them, and elsewhere in the room, nobody would hear a thing … This was caused by the arches in the vaulted ceiling, which he noticed immediately.
He heard the slightest wrong note even in very large ensembles. As the greatest expert and judge of harmony, he preferred playing the viola, with appropriate dynamics. In his youth, and until he was approaching an old age, he played the violin cleanly and penetratingly, and with it controlled the orchestra better than he could have done from the harpsichord. He perfectly understood the potential of all the stringed instruments, as evidenced by his solos for violin and cello without accompanying bass. One of the greatest violinists told me once he had come across no better music for training good violinists…
Thanks to his skill at harmonising, on more than one occasio he accompanied trios on the spur of the moment and, being in a good mood, and knowing the composer would not object, using the sparse continuo part placed in front of him, converted them into complete quartets, amazing their composer.
When he listened to a rich and multi-voiced fugue, after the first entries of the subjects he could tell what counterpoint devices could be applied, and which the composer ought to apply. On such occasions, when I was standing next to him, and he had told me his surmises, he would joyfully nudge me when his forecasts were fulfilled.
He had a good penetrating voice, with a wide range, and a pleasant manner of singing.
Cited in: Dowley, Tim (1981) Bach. London: Omnibus Press, p.123.