According to a post by Scott Crandall on Violinist.com on September 29, 2005,
“…I am a returning adult student. I could not tell if my notes were in tune, I could tell if someone else’s notes were in tune, but not mine. There is a chain on this website where a professional violinist tells how he had trouble playing in tune, but when he used headphones in the recording studio his intonation was fine, [his] solution was to use an earplug in his left ear. After reading that I did some research. I found many articles dealing with hearing problems in violinist’s left ear, seems we subject our left ear to decibels that would not be permitted in Factory environments (up to 115 decibels). I also talked to my daughter’s vocal professor who had data that our right ear reacts faster to musical tones than our left.
“To make a long story short I began using one foam ear plug in my left ear….what a difference in my intonation, no more scratching noises in my ear from the bow, you would not believe how loud and distracting that is until you don’t hear it anymore. Since using the earplug I can hear my Intonation. I may not be hitting all notes correct initially yet, but now I know when they are incorrect and can make the correction needed, right away. My first lesson with the ear plug, blew my instructor away…we had been fighting intonation problems for 3 months to that point, he’d told me he didn’t know what else to do that maybe I had a physiological problem… well I did. Now I am making progress and I like to hear myself play. Periodically I don’t use the plug as an honesty check… the result convinces me all over again that the plug works. It may not be your solution, try one earplug in your left ear, see if that helps.”
So, what of this miracle plug? I confess I was initially skeptical, because I knew that using a practice mute similarly cuts out the resonating harmonics (and a few decibels) of a bowed string, in effect dulling the sound. And, for me, I actually found myself losing my sense of accuracy when playing with a heavy practice mute (see a similar complaint by Larry Brandt).