In the middle of an typically lyrical solo on Canned Heat's "On The Road Again", Al Wilson hits a G in the midrange of his A harmonica.
A standard diatonic in the key of A has a G#, but no G built into it. It is not possible to bend the G# in this octave, so how did he do it?
Several suggestions have been put forward. Perhaps he played an overblow? That is possible as other players around that time were starting to discover overblows and the hole 6 overblow on an A harp would give you a G. However, the slide down from this note includes a very quick slur over the D (5 draw) and the B (4 draw). If he had to switch between an overblowing and drawing, there would be a slight hiccup in this phrase. Several people who knew Al Wilson said that he would sometimes weight the tip of the 7 draw reed to lower its pitch by a semitone, however if this were the case, then that slide down would include an F# (6 draw) and listening to it at slow speed indicates there is no discrete F# note present. Another explanation has been given that he added a valve to the outside of the 7 blow reed, enabling him to bend the 7 draw down to a G - this would also mean that a slide down from this note would include a discrete F#.
The explanation is that he retuned the 6 draw reed, raising it by a semitone to give him the G. This is consistent with the notes of the slide down from that note, as you can hear on this slowed down clip:
Wilson is playing the retuned 6 draw to give a G, which he then bends down to a rather flat F#, followed by the D (5 draw) and the B (4 draw). He used a similar tuning on other tunes, such as "TV Mama" and "Nine Below Zero".
So, one of the biggest pop hits to feature blues harp, is also one of the first recorded examples of a custom-tuned diatonic. If for some bizarre reason you don't have a copy of this tune, it is available on various albums. Click here for more details from Amazon.com of the excellent compilation "The Very Best of Canned Heat", which includes this track and lots of other good stuff.
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