@Leana

The player in the video obviously had SOME bow hair left. I can tell as my own bow maker of 1600s style bows, that 120 bow hairs are certainly not necessary. I read, in the Ottoman-Turkish empire they put under 30 hairs on their bows. Personally, I came to the conclusion, 40 hairs are right for me. Of course you can smear sirup (that's how they invented primitive string instruments in stone age) on whatever stick and get some sounds out of a violin, but the quality will be very poor. I experimented with monofil too, which was extremely difficult. It worked best with my a very cheap monofil thread from my sewing box--the response is good, but the sound is not as nice as with horse hair. Generally, it's said on the net, synthetic bow hair sounds rougher and not as sweet as horse hair. I am supposed to believe that after my personal experience.

@farmboy

The problem with cheap bows is mainly the weight. Making a modern bow as light as possible, takes more afford, which will certainly make the bow more expensive. I started with a 79.00 Euro violin and found the bow awfully heavy. If you rehair such a bow with high quality hair, the sound will be great, which wouldn't solve my problem. Baroque bows are even more expensive than normal bows, so I became my own bow maker. The HAIR is the most important part of the bow! Low quality hair is bad, but if you use high quality hair too long, that's bad as well. Some people never have a rehairing for years and insist they wouldn't need to, but frankly I think these people are crazy.

Generally it's a good idea, to suspect the bow and the bowing first, if the sound is not right. I have been suspecting my fingers on the fingerboard for months, assuming, I wasn't pressing down the strings hard enough. Some self-declared violin tutor on YouTube told a commentator, "Your're probably not pressing down the string enough." Unfortunately, I took this seriously which was fatal for it makes playing a painful cramp, and if I cramp my fingerboard arm so much, my bow hand will cramp too. My whole body was not relaxed, which is always good for producing nasty scratchy sounds. I think, scratchyness is a question of not playing in a relaxed fashion. Too much rosin will make scratchyness likelier. Maybe a professional player will play without scratches, using too much rosin--but that's certainly not me. From time to time I even wipe rosin dust of my strings, for it gets scratchier, the more dust builds up there. People have been asking me, "Why the heck are you doing that?" Well, call me crazy, but I find the tone sweeter and cleaner after wiping the dust off.

Frankly I know my limit and quick pieces are not involved there. If you take time, to experiment with slow, long notes, you will likelier produce a nicer tone. The faster the tune is, I'm playing, the less I will be able to relax. To a beginner, a medium tempo is probably already too fast. So, if you force yourself into fiddling Tom Dooley in a medium tempo, this might be rushing yourself too much. I would rather think of an extremely depressed Tom Dooley, who is singing very-very slowly. Which always was my strategy at the start: playing as slow as possible. After all you have to solve several problems at one time. Keeping the bow in the right place, hitting the right sting at the right place and finding the right bow ankle without touching strings nearby. In the hour when I started I was certainly able to get single sounds out of my violin, which were quite nice. But I was not able to play clean phrases. Which was a long-long waiting game over weeks and months to come. It slowly gets better, but not by forcing myself into progress. We have to take time and relax before playing a note or a phrase.