This is what the preface says (at the last edit)
"The songs in the current volume were selected to represent the very best examples of the genre of the parlour song. They have been arranged for guitar and voice from the original piano-vocal editions. In the interests of authenticity, all of the original markings for tempo, dynamics and expression are exactly the same as on the original song-sheet. It was the norm to produce the songs in multiple keys to suit the range of the vocalist. In this book, guitar-friendly key signatures have been chosen; avoiding multiple flats. A vocal range is offered that can be performed by the majority of singers - all of the songs sit within the range of G below middle C, to the E on the top space of the staff, with the exception of a solitary high F in Roses of Picardy. Male singers will perform the songs an octave below this range.
The piano allows up to ten notes to be played simultaneously, the guitar only six (if strummed), or four if plucked. The aim was to, wherever possible, reproduce the original piano accompaniment – the emphasis being on transcription rather than arrangement. Compromises have been made to the often thick chordal texture of these songs. However, the general harmonic intent has been maintained. Chords have generally been kept in the same inversion bass-lines have been maintained wherever possible. The exact voicings have been adapted to suit the idiomatic nature of the guitar. The guitarist may want to simplify further still – these arrangements act as a reasonably authentic starting point for a performance. "
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