I'm 15. I started violin in4th grade. I am in tenth grade now. I am very bad at sight reading music especially complex rhythms. This is not a mental deficiency because I'm gifted. Usually it is way easier for me once I hear it first. Actually I used to play piano and I was never good at reading notes and rhythms and I really used my ear a lot. Why is this? Is this normal?
Yes, this is normal. Like any other ability, aptitude varies wildly no matter your skill in other areas.
Learning to read music is similar to reading language for the first time and should be approached the same way — start small, with simple things, and work up via lots and lots of practice. While you might pick up the odd tip or trick here and there, there won't be any substitute for hard work.
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It is too normal. Generally speaking, if one can hear something and play it back, then the sight reading tends to take a back seat. Conversely, if one happens to be naturally good at sight reading - it happens - why should they do anything different? The dots say what to do, good enough! Joking apart, I have played with only a handful of musos who were equally good at both, out of hundreds. Both have their plus points, depending on the situation, but it's worth the effort to be able to do both well. My sight reading is average at best, but mostly I play in situations now where sheet music isn't seen too often. Maybe that's a Catch 22 situation, though, and if the reading was excellent, I'd do more of it...
There have been a couple of other questions here that allude to the same syndrome, sorry, can't find them.
I played guitar for 45 years. I first learned everything by ear. My playing stagnated over time, because I had developed a lack of discipline or rather didn't have enough new ideas or tools in my tool box to grow as I wanted. It wasn't for lack of trying either as many times I would average 10 to 14 hours of practice a week for many years.
Along came my interest in reading and understanding music theory. I had no idea at first how much this would open up my ability, thinking and creativity. In my mind I had not matured in the 20+ years at all. In fact I later became so enamored with music theory that I no longer needed an instrument, as just studying the written components was as pleasurable as playing it. In fact it was more enticing because now I could read what someone was doing, regardless of my ability to play it. Not only that, my hearing music became much more in depth as I could now pick out the changes knowing how they were doing what they were doing. My study of intervals also allowed me to see a guitar chord clear across the auditorium and know exactly what it was based on shape alone.
My depth of understanding increased dramatically by the discipline of study, I encourage you to do the same.
In general, playing in ensembles, large and small, is helpful. You're forced to keep going. If you miss some notes, it's okay -- as long as you know where you should be.
Sightreading in orchestra is different from sightreading in chamber music, where each participant is a soloist. It's helpful to give yourself lots of opportunities of both types.
To get better at reading rhythms, it is helpful to just sit in a comfortable chair without the violin and chant the rhythm of a piece. In other words, "sing" the rhythm but without pitches.
In addition to pieces written for violin, some snare drum method books have suitable material for this pitchless sightreading. You have to choose carefully though, because there are snare rhythms that are too esoteric and specialized for the rest of us.
If you could work with a friend occasionally, someone who's good with rhythms, it would be helpful. Good choices of syllables for certain note values and combinations will make it MUCH easier. But there's no way I can catalog them for you. You can pick these up from someone who has already figured out some good syllable combinations that work well.
I will give you an example, though. Sixteenth notes are easier to tarara if you say something like Ta-ka-ta-ka etc.