This category seems un-defined. 1) should low-voice songs not specifically for bass be included here or in another category? 2) should all large works with solo quartet be included, or only those with an aria (I can't see why most Mozart masses should be here) or only those with Bass as the only/main soloist?. Richard Mix 11:24, 8 January 2010 (UTC)
This category is indeed defined and is a subcategory or Solo vocal music (it currently appears at the top of the second column of the listing of subcategories). To answer your other questions:
Solo low is for works for unspecified low voice (e.g. alto or bass), Solo medium is for works with unspecified medium voice (e.g. mezzo or baritone), and Solo high is for works with unspecified high voice (e.g. soprano or tenor).
This is more difficult to address, since it has been applied inconsistently across ChoralWiki. But my opinion is that, for example, Solo Bass, Solo SB, or Solo SATB should only be applied if the work contains a stand-alone movement/section (ie. without any supporting chorus required) of the work for Bass solo, Soprano-Bass duet, or SATB soli (quartet), respectively.
Furthermore, if the work contains several such stand-alone sections (eg. S, A, and T solos, SA and SB duets, SST and TTB trios) then the Solo vocal subcategory should be specified simply with the smallest collective distribution of such solo voices (ie. SSATTB solo in the example given).
Moreover, any given solo voice which only appears in sections with choral support should be placed in the appropriate subcategory of Choral solo music, eg. Choral bass solo.
There could be some ambiguity between these two points just mentioned. For example, the Mozart Missa Brevis in D minor, KV 65 is specified in the Gibson CPDL edition as being for "SATB Soli & Chorus..." which would suggest only the categorization Solo SATB. However, the only (marginally) stand-alone solo section is the SA duet Benedictus which concludes on the dominant (A major) – the subsequent tutti "Hosanna" is tacked on at the end. So this work might be properly categorized in Solo SA and either Choral solo SATB or Choral solo TB; alternatively, some might feel this should be categorized only in Solo SATB, since the only additional appearance of solo voices is alone or in combination with other solo voices, albeit within movements which also have choral subsections. My own preference in this case would be simply to use the latter categorization (Solo SATB), on the grounds that at least some of the voices (SA) appear in (essentially) stand-alone solo movement (the SA duet), and all four voices (SATB) only appear elsewhere with no chorus part(s) singing at the same time.
Possibly, we have been guilty of "slicing the bologna too thin" (ie. trying to be overly specific) in these categorizations. The original intent was to allocate solos which appear in works/movements requiring additional chorus support to categories different from works/movements requiring only soloists. This works well when one is dealing with a single work but becomes more difficult to treat when there are several movements/sections of a larger work with varying disposition of solos (choral and stand-alone). My current feeling (perhaps different from that I had when these categorization principles were first applied) is this:
If a larger scale work with several movements/sections has at least one section which requires (stand-alone) solo voices, then all solo voices (including those which might otherwise be considered as choral solo voices) be considered as (stand-alone) solo voices for the purpose of categorization. In other words, in the Mozart example cited above, Solo SATB would be the only (and simplest) categorization.