If you have a spare lower end guitar (25 ½” scale) sitting around doing nothing and have always wanted to try a baritone guitar, then do the following:
Install a set of heavy strings. Acoustics = .014-.059 Electrics = .012-.060
Tune to C Standard tuning. Songs in the key of C work extremely well because you can use key of E chord shapes, as does the key of F where you use key of A chord shapes.
Drop D would now be Drop Bb, and lets you play in the key of Bb using D chord shapes.
Swap out the 3rd and 4th strings to get ½ Nashville Baritone tuning:
3rd string: anything .010 thru .012 for acoustics, .008 thru .010 for electrics
4th string: and .015 thru .017 for acoustics and .013 thru .015 for electrics.
You can go down to B Standard tuning, but it gets a little loose. If you’re playing with a keyboard, they typically like the keys of C, F, and Bb. This is also a fantastic exercise for transposing on the fly. Also, if playing along with several other guitars it gives you some very unique voicings and isn’t muddy in the mids.
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Below is some handy information about vocal ranges as found on guitar from perplexity.ai
Low Strings
The low E (6th) string and A (5th) string of the guitar generally fall below the range of most voices, especially in the open position. However:
The 12th fret of the low E string produces E3 (164.81 Hz), which is within the range of bass and baritone voices.
The open A string (110 Hz) is near the bottom of many bass vocal ranges.
Middle Strings
The D (4th), G (3rd), and B (2nd) strings cover much of the typical vocal range:
The open D string (147 Hz) is in the range of many male voices.
The G string, especially when fretted, covers notes common to tenor and alto voices.
The B string (247 Hz open) is in a comfortable range for many female voices.
High E String
The high E (1st) string, especially when fretted, covers the upper ranges of most voices:
The open high E (330 Hz) is near the top of the typical male vocal range.
Fretted notes on the high E string can reach into soprano territory.
The 12th fret on any string produces a note exactly one octave higher than the open string.
The 5th fret of any string (except the G string) produces the same note as the open string above it.
A typical trained singer might have a range of about 2 octaves. On a guitar, this could be represented by:
The notes from the open A string (110 Hz) to the 7th fret on the high E string (440 Hz) for a low voice.
The notes from the 5th fret on the D string (196 Hz) to the 17th fret on the high E string (784 Hz) for a high voice.
Remember that exceptional voices can extend beyond these ranges, just as skilled guitarists can utilize extended range techniques.