I like to use my iPhone’s slow-motion camera to catch any technical inconsistencies that happen at speeds where such factors are hard to monitor. Here’s an excerpt from William Walton’s first Bagatelle for guitar. I was working on my alternation pattern at the end of the work. In real time it looks like this:
Here’s the same passage in slow motion. Notice the alternation (I and M fingers pass each other at the neutral position – helping to keep the pattern rhythmically accurate).
I made the slow motion video because I was looking for a breakdown that was occurring in the passage. After noting that my alternation was fine I realized the problem was in the left hand – that saved me a lot of wasted practice time.
In any case the use of slow motion video is a great way to break down problems that are too detailed to see in real time. In some cases I film passages played at the very top of my tempo range (or beyond) to find what is creating a barrier; is it technique or just the extent of my abilities?
Try this yourself. Even if you don’t know what you’re looking for with regard to the sympathetic or alternation patterns you can at least look for a uniformity. Are your fingers moving with the same excursion? Are they moving in time? Do they look coordinated? Its all there under the naked eye of the slow motion camera!