Why Is Portamento More Than a Blurred Connection Between Notes?

Portamento carries sound continuously from one pitch to another. The voice, unfretted strings and the trombone can make pitch genuinely move between two points. A piano cannot: its pitches are separated into discrete keys. Usage overlaps with glissando in different traditions, but portamento usually emphasises the act of carrying one note towards another, while a glissando often makes the intervening pitches more explicit.

A good portamento does not give equal weight to every pitch in between. It has clear points of departure and arrival, and its expression comes from when the movement begins, how quickly it travels and where it accelerates or settles. If the destination loses focus, the melody becomes slack. If every shift leaves the same audible trail, the phrase turns into a repeated emotional mannerism.

Nineteenth-century teaching sources and early recordings show that portamento was once an important expressive resource in string playing and singing. Changes in taste and recording culture during the first half of the twentieth century made it increasingly restrained. Frequent slides in old recordings should not simply be heard as untidy technique, while removing every slide today is not automatically more faithful to the score. The real question is whether the movement serves the melody’s direction and the work’s language.

The piano cannot reproduce continuous pitch, but it can learn something from portamento about phrasing: the time between two notes is not empty; it has a destination. When listening to strings, notice how a slide leaves the first note and arrives at the second. That reveals more than merely deciding whether a slide is present.

https://www.cambridge.org/core/journals/journal-of-the-royal-musical-association/article/bowing-styles-vibrato-and-portamento-in-nineteenthcentury-violin-playing/5E8C582B69188CFF66F5F733F6E319C3
https://www.tandfonline.com/doi/abs/10.1080/01411890600860733
https://www.phys.unsw.edu.au/jw/reprints/portamento.pdf