In July of 2002 I discovered, by a process of trial and error, a completely new approach to two-handed tapping. Two factors lead me towards this realisation.
The essential question I needed to address was What are the usual sources of inaccuracy in the technique of guitar players who use tapping in their playing? I realised that the use of legato technique, which uses both pull-offs as well as hammer-ons was responsible. Usually the first sound in a legato passage is the loudest and fretting the string from above gives accentuates the note concerned. Very often the note that is stressed most strongly is not the one that, for the purposes of musical expression, ought to be. Additionally there is a difference in legato playing on bass strings and on the treble ones. Also we play legato in a different way at the first position than, for instance at the 18th position where the frets are closer together and where more notes can be played on each string. Stanley Jordan, in one of his articles about two-handed tapping, mentioned that when we play legato we can always hear the movement from one string to another.The second factor which influenced my thoughts was my analysis of recordings and musical philosophy of Glenn Gould. Everybody who has listened to him playing Bach's music can attest to the clarity and purity of his performances. There is no place in such music for the inaccurate dynamics that the usual approach to tapping can introduce. Additionally it is very important to separate the sounds played in a sequence with rests. This kind of playing is called portato technique and is often neglected during the process of learning how to play piano by those who prefer legato technique, where notes are not properly separated by rests.
For these reasons I decided to start playing portato in preference to legato. I am pretty sure that it is not something unique or even new but I haven't come across any description of this kind of tapping on the famous tappers' internet website yet link to site And not even Stanley Jordan has mentioned these issues in his article link.
Portato technique resembles legato technique in producing smooth, evenly-toned notes but unlike legato every note is separated from the next by a very short rest, a characteristic of staccato playing. Unlike staccato technique where notes are always short and loud portato technique includes notes of various durations and volumes. The idea is that every tone is played with a hammer on and doesn't use the energy of the previous note to supply its volume. After hammering on each finger is taken away from the fret and allowed to dampen the string (which is uncommon in traditional technique). The next sound is only made when the previous note has ended. Of the approaches to tapping it is the portato technique is the furthest removed from traditional guitar playing (using the pick or fingers).
We should ensure that the rests between notes are as short as possible. Attention to the use of such rests is often an important part of accurately performance any piece of music irrespective of whether the guitarist is tapping or if they pick or strum each note.
Portato technique may seem to be uneconomical it requires more finger movements. Additionally taking away our fingers after each note may slow down some passages but less physical strength is required for playing portato than for playing legato because there is no need for a powerful pull-off or hammer-on to supply volume to the succeeding notes.
In summary portato technique provides a greater degree of control over the dynamics of what is played and there a is less noticeable difference between the volume of notes played on different strings and those that are played on neighbouring strings. This gives us greater control over the dynamics of the whole piece, allowing us to stress chosen notes (something which jazz guitarists like Pat Martino regularly do in their be-bop phrases) which is harder to accomplish using legato.
Portato technique provides great opportunities for the manipulation of the dynamics of any piece of music whether learned or improvised. The music of J. S. Bach where the time plays the crucial part (the best example are the pieces of Glenn Gloud, but not only).
The rhythm of the piece influences its character and should be followed strictly. It is common practice to stress some beats more strongly than others, for instance a common practice when writing music in 4:4 timing is to stress the 1st beat heavily and the 3rd beat slightly so that it is stronger than the 2nd and 4th beats. Often there are no strong stresses in a bar and the rhythm is quite unlike the one you would expect from the designated time signature. Such passages eventually resolve with a strong beat being played where we would have expected one had the rhythm been just as the time signature would have lead us to expect. A good example of this is kind of rhythmic device can be found in "The Goldberg Variations", and I recommend the version played by Glenn Gould. In jazz improvisation it is quite common to stress only the weak parts of the bar, a device called syncopation.
Portato technique will give us a great awareness and fluency as far as manipulation of rhythm is concerned. This is one of the greatest advantage of this technique of playing and it is a pity that most tappers use legato instead of portato technique and don't pay enough attention to the accurate expression of the rhythm of the music they play.
The famous polish tapper Zefir uses a similar approach in his cross-handed tapping As Zefir wrote "There is only a little legato in crossed hand technique, all sounds are articulated with fingers, which is similar to the playing with the pick."
In the guitar technique trills are usually performed on one string using legato technique. Such trills are idiomatic of the guitar and there are no keyboard instruments with such a smoothness of trill. The baroque period was typified by the abundance of ornaments (including trills) which were often played on keyboards instruments such as the harpsichord which produced notes of even volume, quite unlike those we would get from playing legato on guitar. The halftone trill in this kind of music consists of strong, separate sounds, more like those we get when applying portato technique to guitar.
To make the sound and idea of portato more clear I recorded few tunes (for example two-parts of J. S. Bach's Invention in A Minor (nr 13, BWV 784)), which you can download from my video section. If you try and play this piece yourself then be careful to take the index finger of your left hand away from the strings.