The Violin Concerto No. 1, Op. 6, was composed by Niccolò Paganini in Italy, probably between 1817 and 1818. The concerto reveals that Paganini's technical wizardry was fully developed. Contemporary audiences gasped at the extended passages of double-stop thirds, both chromatic and in harmonics.
Paganini intended the Concerto to be heard in E-flat major: the orchestral parts were written in E-flat, and the solo part was written in D major with instructions for the violin to be tuned a semitone high (a technique known as scordatura) so that it would therefore sound in E-flat. This enables the soloist to achieve effects sounding in E-flat, which would not be possible with normal tuning. An example of this is the opening of the third movement, where the violin plays a rapid downward scale A-G-F♯-E-D, both bowed and pizzicato, which is possible on an open D-string, but extremely difficult in the key of E-flat (i.e. playing B♭-A♭-G-F-E♭) because two strings would be required to play this downward scale, whereas only one string is required to play it in the key of D. In addition, having the orchestra playing in E-flat appears comparatively to mute the sound of the orchestra compared to the solo violin, because the orchestral string section plays less frequently on open strings, with the result that the solo violin part emerges more clearly and brightly from the orchestral accompaniment.
Contemporary audiences did not realise that Paganini had retuned his instrument, and were thus all the more amazed at what he appeared able to play. (The more musically adept members of the audience would have recognised the distinctive sound of a violin's open string, and would have observed that this fell on the keynote of work (E-flat), and would have therefore realised that Paganini had re-tuned his violin.)