Long time bass [hack] player, also play a little bit of guitar, working on learning some music theory to expand my understanding of the mechanics of creating music. I'm curious about open tunings on both bass and guitar. Since I have a strong fondness for blues & slide guitar, I'm finding more and more references to open tuning. What are the major reason(s) for doing this? Can open tuning(s) be used on the bass as well as the guitar? Thanks for the assistance -d
There are a couple reasons that one might use an open tuning but the most common has to do with chords. As you may well have noticed, certain chords are much more comfortable to play than others and some chord voicings just can't be accomplished. Open tunings allow chords to hold a different shape on the guitar, which can make some chord voicings easier or actually possible. Open tunings or alternate tunings can also allow for some monophonic lines to be more easily played and can be used to allow open strings to be incorporated. Some will also say that open tunings will change the tone of your instrument to some extent, which is certainly true since you're essentially changing the tension of the strings, which affects tone, but most professionals will have their alternately tuned guitars all set up for that specific tuning; a setup of this nature would usually change the gauge of the strings to accommodate the needed frequency and maintain the instrument's intended tone and sustain, as well as considering the tension that the strings put on the instrument.
In a traditional approach, the bass doesn't typically play chords, so most of the value of an open tuning is lost, but not all of it, though it may just be categorized as an alternate tuning without playing chords. Since the bass is usually playing monophonically, your alternate tuning considerations would be focused on playability and whether or not you want open strings included. If you are consistently playing certain types of patterns that are hard to accommodate on the bass, an alternate tuning might be able to help with that. This could also be a means of writing something different than you usually would (if you're writing), as we humans tend to fall into habits/patterns and those patterns are often influenced by the amount of effort/comfort involved in accommodating them. So, a change in tuning will make some options easier and others harder, essentially forcing you to either do something new or find a new way to do the same thing you did in the original tuning, both of which can be a great exercises for your musicality, and your brain in general.
There are those bass players that play chords, myself included, and an open tuning could very well be great for those players. Beyond the fact that low frequencies tend to get very muddy when used for chords, bass is a lot more difficult to physically play chords on due to the size of the instrument and its strings, as well as the scale length being longer, making it more difficult to get the same fret range that you would on a guitar. An open tuning or alternate tuning could help reduce the physical strain of accommodating chords by allocating some notes to open strings, or changing the location of a given frequency to be included in your chord, which can reduce the stretch needed to reach it, or make a given note not need to be barred, as barred chords on bass are particularly uncomfortable.
So generally speaking, I don't typically see open tunings for bass, though I have seen alternate tunings. For example, the bassist for Tool uses DADA (not sure if he always does or just for some songs though). I also have a 6-string bass that is tuned from D-Eb (tuned in fourths) but that just affects the overall range of the instrument and not the playability or comfort level of a given chord or interval. It could be fun to experiment with but if it were more useful, it would probably be a lot more common than it is.
tl;dr; "open-tuning" means that the open notes are in key (are in "tune").
If you're mostly into blues, then you're probably looking for interesting tunings for a blues minor pentatonic scale. In this case, I'm inclined to agree with @Basstickler. If you'd like to play around with other scales, you might be interested in a open tuning for that scale.
Check out this image (that I borrowed from this answer):
I will mainly talk about guitar here, but we'll never mention a chord, so this all applies equally well to bass. To relate this to bass, just look at the EADG strings.
These notes are in the A minor pentatonic scale. There are two cool things about A minor here - it's very popular in blues music and it has a lot of notes that happen to be open on a standard guitar tuning. This last feature makes playing in this key extra-flexible because you can now hit notes that might be otherwise be difficult to reach from a given position, and also extra-forgiving, because you can always just stop fretting and keep strumming/picking/slapping away and you're still in key.
Of course, A minor pentatonic isn't the only scale that has lots of open strings on a guitar or bass. There are other scales as well. More to your question, there are also many keys for which notes on the open string are not in key. They're way out of key. One example of this is Bb minor (check out that 1st fret in this image that has exactly 1 note [or 0 notes for bass]). This means that you basically gotta have your fingers on the board at all times when playing Bb minor.
However, if you tune each string on your guitar up by one half step (E# A# D# G# B# E#), then Bb minor has lots of open strings. In fact, it's all the same fingerings as A minor was in standard tuning. Bb is A plus one half step!
Similarly, from the picture we see that A minor has one string (B) for which the open note isn't in key. You could make it be in key if you liked, by simply tuning that string up one-half step (imagine moving the whole B row in the image one step to the left). Now we can also pluck the B (now the B#) string open and be in key. Of course, this maybe complicates other fingerings you'd like to have in this scale.
This "open-tuning" thing doesn't only work for the minor keys, though. There are many, many, many well used and loved scales. Some of these may coincide with having many or all of the open notes in a standard tuning. Many more will coincide with having many or all of the open notes in a custom tuning, if you'd prefer having open notes be in key.
One reason for alternate tunings, especially with slide guitar, is to reduce the interval distance between strings, so that a melody or scale can be played with less movement of the slide. This can also be an advantage on bass, where the scale can make it hard to reach some intervals.
I was playing slide guitar with Open-D (Vestapol) tuning [DADF#AD] when I picked up bass, so I ordered a custom set of bass strings from Kalium to tune the bass [DF#AD]. (Intervals between strings are major third, minor third, and perfect fourth.) Worked well for me, being familiar with the chord shapes already. Of course it makes it less convenient to reach wide intervals, but I generally prefer close intervals anyway.
From a slide perspective it becomes obvious: a slide is straight, so complex fingerings are impossible. Instead, you tube the strings so that the chords you want are able to be "fretted" by a straight bar.
Even if not using a slide, open tunings can sound quite different when you play chords.
Yes, you can use open tuning on a bass - it's not quite as relevant, as basses are tuned quite simply (guitars are tuned the way they are to make chords very accessible, and this isn't as necessary on a bass)