So in the late 19th/early 20th centuries, chazzanus, or cantorial music, had a major surge of popularity not just as something done in the synagogue during prayers but as an art form in and of itself, and the chazzan (cantor) was seen as an artist. People would go to concerts- or even operas- to see a chazzan perform, buy records of chazzanus, etc. Specifically the interwar period became known as a "golden age" of chazzanus, and one of its stars was Yossele Rosenblatt, who not only made Jewish history as a chazzan and performer but ended up making movie history as well as one of the first people ever to have his voice heard in a major motion picture.

Josef Rosenblatt (Yossele was a diminutive) was born near Kiev, in what was then the Russian Empire, in 1882; he came from a religiously devout family of chazzanim, and was the first son in his family after nine daughters, with his father immediately seizing on the opportunity for the family vocation to be carried on. Already before the age of ten he was known as a wunderkind, performing alongside his father at synagogues throughout Eastern Europe despite never having received formal training. At age seventeen, he was performing in Vienna concert halls; at age eighteen, soon after his marriage, he beat fifty-six other candidates to become the chief chazzan of Pressburg, and five years later he moved on to Hamburg. He was, throughout this time, extremely successful, and soon became the breadwinner not just for his own growing family but for his parents and siblings; he was not just performing, but producing phonograph records as well.

In 1911, he and his family came to the United States with an invitation from Congregation Ohab Zedek, an Orthodox synagogue in Harlem, to serve as their chazzan. In addition to his tenure there, where the services he led were phenomenally popular, he became well known as a concert performer in the Jewish community and beyond, as well as becoming a singer of choice for charity benefits; in 1917, he headlined an event raising money for Jews suffering in Europe due to the effects of WWI, with a packed audience of 5,000 and a quarter of a million dollars raised. This event was only the first of a series of nationwide concerts raising money for the cause, which became notable when it led to what Rosenblatt's son considered, in his biography of his father, to be a turning point in his father's career: after a benefit concert in Chicago, Rosenblatt was asked by the director of the Chicago Opera Company to star in a proposed production of the opera La Juive, for which he would be paid $1,000 per performance. While Rosenblatt was initially amenable after hearing that his initial conditions- that he would not have to remove his beard, that he would not have to perform on Friday or Saturday, and that the subject of the opera was befitting a religious Jew- would be met, he then turned the offer down, stating that he and the synagogue which he served did not believe that it was befitting for him to perform in operas.

This led to an explosion in Rosenblatt's fame and career. The story was covered in the New York Times; the music magazine Musical America praised the decision as a matter of sacrificing mere lucre for religious belief. However, this certainly did not mean that he refused to sing in secular settings, but more that he refused to play a part and sing as anyone but himself, a religious chazzan, even if he was singing some secular material. Only a month after he turned down the Chicago Opera, he was performing to wild acclaim at Carnegie Hall, with audiences eager to see who this singer was who would turn down $1,000 a performance. He became renowned for his performances and for his vocal skill as a tenor as well as his three octave range (which the Los Angeles Times described as greater than that of any living person), particularly his legendary head voice/"kop shtimme." He was proud of the way that his concerts, for Jewish and non-Jewish attendees alike, were familiarizing massive audiences with the music of the synagogue. Enrico Caruso, the famed opera singer, went up to him after his performance of the song Eli Eli and kissed him; the New York Times consistently covered his performances in its arts section as it would any major talent, and he was soon earning massive amounts of money for performing (much of which he gave to family back in Europe and to charity).

However, Rosenblatt may have been too generous with his money, as in 1922 he invested in a crooked scheme by Jews in New York to start a new Jewish newspaper, which led to him being forced to declare bankruptcy in 1925. Still incredibly beloved, he promised that he would pay back all of his debts by performing; unable to be quite as choosy in his venues, he entered the world of vaudeville. He became a wild success on the circuit as not just a novelty act but an extremely talented one- he only performed on an empty stage and in his cantorial or religious garb, and upon completing his set would immediately walk out of the venue, not even staying for the generally raucous applause. He accepted $15,000, a massive amount of money, to lead the High Holiday services at a synagogue in Chicago. He was soon crossing the United States regularly to perform, though always refusing to appear on Friday and Saturday.

In 1927, Rosenblatt was in Los Angeles on a vaudeville tour when he entered a brand-new kind of performance- being recorded on the new Vitaphone technology, the first broadly used technology for synchronizing visual and audio performances. He was recorded for several shorts, singing some of his most popular pieces, but then was approached by Al Jolson and the makers of a new film, the first "talkie," The Jazz Singer. The film, based on a short story and play, would be about Jakie Rabinowitz, the son of a chazzan, who then goes on to be a popular vaudeville singer named Jack Robin, trying to balance his family, relationships and new career- which comes to a head when his father is dying on the night of Yom Kippur and the congregation begs Jakie/Jack to come back to the synagogue and sing Kol Nidrei for them. The story was actually explicitly written for Al Jolson, but it's actually hypothesized by some that the character of his cantor father was based on Rosenblatt, which would explain why he was offered the role, apparently for $100,000. Rosenblatt turned this down, refusing to play a character, but did agree to be featuredin the film playing himself, singing at a concert. (According to something I read, Rosenblatt also dubbed the father's singing, but I can't find any indication that this is true elsewhere.) His participation in the film was hugely advertised, with Rosenblatt receiving fourth billing after Jolson, the actress playing his love interest, and the actor playing his father; the souvenir program for the film also stated that Rosenblatt gave advice in the film on how to make synagogue scenes as accurate as possible. Some see Rosenblatt's role in the film as being a sort of middle, mediating ground between Jakie and his father- someone who is able to both sing for the public in public places and sing holy songs. However, for the average person, the importance of Rosenblatt is simply that he was one of the very first people whose voice was ever heard in a major motion picture.

While it had seemed like Rosenblatt was regaining his former stature as a performer, not to mention financial security, with 1929 came the Great Depression, which became a death knell to his chances of earning a living leading services at synagogues (which could no longer afford to pay him), which had always been an important part of his work. He was soon grasping for any opportunities which he could use to support his family, and in 1933 was given an opportunity that must have seemed like a dream- to finally go to the Land of Israel in order to sing for a film being made of various holy sites across Mandatory Palestine for the American Jewish public. While in Palestine, Rosenblatt also served as a chazzan at a number of synagogues and performed concerts to new appreciative audiences- apparently, the great Zionist writer Chaim Nachman Bialik loved Rosenblatt's Shir HaMaalos so much that he wanted to make it the anthem of the Jewish State. The film had just been completed when Rosenblatt suffered a fatal heart attack on June 19, 1933; he was buried on the Mount of Olives in Jerusalem, as had always been his wish. At his funeral, the chief rabbi of Palestine, Rabbi Abraham Isaac Kook, eulogized him, and two other famous chazzanim, Zavel Kwartin and Mordechai Hershman, sang; a few days later, at Carnegie Hall, the Cantors' Association memorialized him (despite having earlier cast aspersions on him for his vaudeville career) with a massive concert in which 200 fellow chazzanim sang one of Rosenblatt's compositions; the concert was a benefit to raise the money to bring Rosenblatt's widow and son back from Palestine, where he had been stranded.

Today, few remember Rosenblatt, despite how famous he was in his lifetime; however, to those who know chazzanus, Rosenblatt will always be known as someone who stood out as the great in a sea of the many great chazzanim of the "golden age." While his tunes are used more in cantorial performances than in the synagogue at this point, the emotional quality of his singing of ritual music- a kind of "sobbing" quality- became incredibly influential.

Blatantly stealing from myself, I give you: Was Classical Music ever the "pop music" of the past? Was it widely popular? Did everyone know Beethoven, Brahms and Bach?

By the time the classical style went out of fashion, around the end of the 18C, a radical shift in paradigm was starting to become apparent in the sphere of what we now call "art" or "academic" music. See, for centuries, large scale music had been composed primarily at the behest of monarchs and nobles, and therefore tended to be incredibly out of reach for most of the population. That didn't necessarily mean the emerging bourgeoisie couldn’t occasionally get to enjoy performances by renowned composers during the classical period, but it wasn’t the norm, folk music would be what we now understand to be “pop” music. But I’m not an expert in European folk, so I’ll leave that bit to my betters.

What exactly is the Romantic period?

Very broadly speaking, it’s an artistic movement. No shit, Sherlock. But seriously though, that’s what it is. In terms that interest us, it’s part of the never ending evolution of art music. Most musicologists agree in determining that it gradually emerged in what is now Germany, largely due to the work of several composers who lived around the same period, and who initially subscribed to a movement known as the Sturm und Drang, which is German for Storm and Drive, although it’s also referred to as Storm and Stress.

The core principle was based on opposing the traditional ideals of the enlightenment: while the enlightenment principle of reason as the basis for all creation had influenced artists to compose music based in grand, emotionless structures, reflecting techniques and virtuosity above all else, this movement, proposed by several writers such as Johann Wolfgang von Goethe and by composers like Johann Baptist Vanhal and Carl Ditters von Dittersdorf, implied abandoning reason as the basis for art, focusing instead in the freedom and expressivity that emotions allow. And so, new composition styles arose, which favor change instead of rigid structures; melody takes preeminence, which can, like a storm, change drastically in just one set of notes, one single measure. The result gives us unpredictable pieces, with sudden shifts in tempo, and the incorporation of mechanisms like the tremolo, a technique consisting in adding gravitass and emphasis to the melody through strong vibrations in the strings. Oftentimes, compositions written following this style are in a minor key, which typically serves to demonstrate deep and often dark emotions and feelings.

This style was instrumental in the development of Beethoven’s new wave of pieces that, starting with his Third Symphony, the Eroica, drifted away from the classical structures imparted to him by Joseph Haydn, one of the most influential classical composers and his teacher, focusing instead on emotional elements. Other contemporaries of his who became more and more interested in leaving the overly rigid structures of classicism behind, such as Louis Spohr, also German, renowned as one of the greatest violinists of his time. Most of his compositions are for violin as soloist, and many of them include the harp. Why is this relevant for this emotional component? Well, ever since he was a child, Spohr had felt a deep fascination for this instrument, which he could not play without feeling incredibly frustrated, due to his deeply rooted perfectionism. When he moved to Gotha in 1805 to take the position of kapellmeister, he met a young harpist called Dorette Scheidler, who was 18 at the time; young Louis fell in love immediately, according to his autobiography. After spending time conducting the orchestra in which Dorette would often play harp, piano and violin solos, Spohr decided to confess his love when, after a private concert from which they departed together alone in a carriage, he held her hands in his own and asked her “shall we thus play together for life?”

They got married and of their marriage two daughters were born, as well as a series of compositions specifically designed either for the violin and the harp, or for the harp as soloist. The motivation and inspiration for these pieces came, according to his own words, from his deep love and devotion to his wife. Fascinated by Dorette's prodigious technical skills, and still an admirer of the instrument itself, Spohr decided, working together with Dorette, that they should design a technique that would allow them to play together, since both instruments are, typically, incompatible. The result was a technique that introduced modifications to the tuning in both instruments, to avoid, when it came to producing sounds at the same time, that the necessary tension ended up breaking the extremely fragile strings of the harp.

But aquatermain, why is emotion relevant if we’re talking about fame?

Because emotionality and nationalism go hand in hand. The 19C is a century that sees the full emergence of capitalism, nationalism, and imperialism. Nation states are showing up everywhere on the European map. Capitalism is starting to delete the aristocracy as the only real big and powerful social class. Wanna know what capitalism and imperialism need to exist in this period? Nationalism. Patriotic sentiment is something rather new to most European nations, since most of them hadn’t even considered themselves to be nations up to this point, at least not in the traditional sense we now understand a nation to be.

Many composers from the romantic period felt a deep connection to their own nations. You mentioned Franz Liszt, and, well, he was definitely one of the precursors of the introduction of nationalistic themes, borrowed from folk tunes and styles, into art music. And my oh my was Liszt famous. By the time he turned 30, he embarked on a set of tours through Europe that lasted, on and off, almost the entire 1840s, mainly because he was one of the greatest pianists of his time, but also because he created deeply emotionally charged music, often rooted in nationalistic Hungarian themes and sounds. Although Liszt spent most of his later years composing and teaching instead of performing in public, he remained a legend, a legend that survives to this day.

A good friend of Liszt's also became exceedingly famous in his time: Camille Saint-Saëns, one of my favorite composers of all time. Born in Paris in 1835, he showed signs of having perfect pitch by the time he was three, learning the basic elements of the piano from his great aunt.

Saint-Saëns received formal piano lessons from Camille-Marie Stamaty, a composer renowned for composing pedagogically friendly pieces, as well as piano interpretation techniques. In spite of Clarence’s initial doubts, his prowess was so great, that he gave his first public performance aged 10, playing pieces by Mozart and Beethoven, marvelling the audience. 3 years later, he was admitted at the Paris Conservatoire, one of the most prestigious musical instruction institutions in the world, remaining to this day one of its most distinguished alumni. There, aged 13, he began composing the first of his almost three hundred works.

After leaving the Conservatoire, between 1861 and 1865, a very much still young Camille started working as a teacher at the Niedermeyer School in Paris. During this period, his teaching post demanded most of his time, and so he ended up resigning in 1865 in order to go back to composing and performing in public, since he barely composed anything during his tenure (with the notable exception of his Introduction and Rondo Capriccioso, dedicated to virtuoso violinist and composer Pablo de Sarasate).

The final decades of the 19C meant a huge uptake on his popularity, rapidly becoming one of France’s most popular composers and performers. By this point, Saint-Saëns, who had been considered to be some sort of reincarnation of Mozart in his youth, had also gained the approval and admiration of many of his peers by this point, including his friend Liszt, and other big names like Hector Berlioz and Giachino Rossini. By the time the 1880s showed up, his fame had crossed the channel, and he became a favorite of the London music scene, travelling with some regularity to England to perform his own works, as well as to conduct other composer’s pieces, where he premiered his Third Symphony in 1886, commissioned by the Royal Philharmonic Society, and eventually dedicated to the memory of his friend Liszt after his death that same year. I particularly recommend listening to this recording of his Third Symphony performed by Letonian organist Iveta Apkalna.

The Red-Headed League

I could go on forever. As an honorable mention, let’s talk briefly about Pablo de Sarasate. He was a Spanish composer who is considered to be, together with Niccolo Paganini, one of the greatest violinists in history. He composed only 54 pieces, because unlike most of his contemporaries, he prefered to spend his days performing in public rather than actually composing.

Sarasate was so incredibly gifted with the violin that he spent most of his adult life touring Europe, North América AND South América, and his fame was so great, that Arthur Conan Doyle included him as an important element in his short Sherlock Holmes story The Red-Headed League. In the story, Holmes interrupts his investigations to go and see Sarasate performing live.

Wanna see something cool? We have a few recordings of Sarasate playing, done at the very beginning of the 20C. Here he is playing the second movement of one his most famous pieces, arguably one of the hardest pieces ever composed for the violin, Zigeunerweisen.

This seems like a good opportunity to drop one of my favorite answers from the past, question dropped by /u/EnclavedMicrostate, wondering how serious this letter was of Elvis asking to be a federal agent.

...

June 5, 1956. Burbank, California: Elvis, charting at number one with Heartbreak Hotel, appears live on the Milton Berle Show, for the second time.

The first time, he sang a ballad. This time, Elvis performs "Hound Dog" with an up-tempo beat. Everything is normal for the first minute and 30 seconds. Then, chaos lets loose.

You can watch here from the start.

The tempo slows down (1:40 signature on the video above). The crowd goes wild. Elvis gyrates. And the world is scandalized. Truthfully, scandalized. Elvis is condemned as immoral. As Milton Berle himself said later, Elvis received "hundreds of thousands" of pieces of hate mail.

As damage control, Elvis ended up doing much tamer followup on the Steve Allen Show on July 1 where Elvis wears a tuxedo and sings to an actual dog, to which Elvis later said

It was the most ridiculous appearance I ever did and I regret ever doing it.

Despite the family-friendly walkback, Elvis's reputation continued to have a transgressive edge with older Americans.

However, Elvis was something of a conservative with law enforcement. He made friends with officers as he toured, and started to collect police badges, which were usually given as gifts; i.e. a deputy sheriff's badge when he was performing in Jackson, Mississippi. He also got a Lieutenant Detective badge from a detective he was friends with in the LAPD (it wasn't "real", a reporter later verified that the badge number never was given to a detective), and even -- just based on word of mouth, he never performed there -- was sent a Constabulary badge from Kent in South England.

...

September 28, 1974. College Park, Maryland: Elvis gives a monologue at a performance, which you can watch here:

Things that are written about me in movie magazines are trash! Rumors that you hear about me are trash!

I'm an 8th degree black belt in karate.

I'm a federal narcotics agent. I am, I swear to god ... they don't give that to you if you're strung out. On the contrary I have to be straight as an arrow ...

By this time, Elvis had been on a steady stream of pills. In 1977, the year Elvis died with 14 different drugs in his system, Elvis's doctor George Nichopoulos wrote prescriptions for ten thousand doses, as he tried to keep Elvis from getting even more pills from other doctors. From a 2002 interview:

Elvis's problem, was that he didn't see the wrong in it. He felt that by getting it from a doctor, he wasn't the common everyday junkie getting something off the street. He was a person who thought that as far as medications and drugs went, there was something for everything.

Even before meeting his doctor in 1967, he had been taking amphetamines (which weren't outlawed in the US until 1965). So, Elvis had been taking medication all his life, but didn't consider his addiction the same as illegal drugs.

I'll get to the Nixon meeting soon, but I'd like to address the "eighth degree black belt" thing, because it helps answer the overall question...

...

Elvis was drafted to the Army in 1958 and his first exposure to karate was on the base he was stationed at in Germany. He earned his first black belt in 1960, and went on to train with Master Kang Rhee in Memphis.

He was genuinely passionate about martial arts, although his seventh-degree black belt (we'll get to eighth in a second) was earned under dubious circumstances. He had gotten up to sixth degree; Kang Rhee was seventh degree, so that was technically the highest Elvis could go.

Elvis very much wanted to be seventh degree (something about it being a "perfect number") so (according to Wayne Carman, who trained with Elvis) Kang Rhee called together a gathering of black belts about the problem; the end result as Kang Rhee being raised to eighth-degree so Elvis could be brought to seventh. According to Carman:

Elvis's gratitude upon his promotion is obvious. After class, Elvis gave Kang Rhee a Cadillac.

So, when Elvis wanted something, he was persuasive. And he did eventually get an 8th degree belt from Kang Rhee as well, on September 16, 1974. (If you're paying attention to dates, you'll notice this is only two weeks before he talks about it on stage.)

...

Let's get to that letter. Elvis was on a flight towards Washington DC and -- by coincidence -- was next to Senator George Murphy of California. Elvis brought up a desire to be a Federal Agent, and the Senator suggested Elvis write a letter. Elvis did so, on American Airlines stationary:

First, I would like to introduce myself. I am Elvis Presley and admire you and have great respect for your office. I talked to Vice President Agnew in Palm Springs three weeks ago and expressed my concern for our country. The drug culture, the hippie elements, the SDS, Black Panthers, etc. do not consider me as their enemy or as they call it the establishment. I call it America and I love it. Sir, I can and will be of any service that I can to help the country out. I have no concern or motives other than helping the country out.

The letter was originally going to be given to Murphy to give on to the president, but Elvis ended up having his driver go to the White House when he landed. One of Elvis's bodyguards handed off a letter which made its way from the Secret Service to John Finlator (acting head of Narcotics) who had nixed the request. It also landed with Bud Krogh, Nixon's deputy assistant for domestic affairs (and an Elvis fan).

Due to Krogh, a meeting ended up happening six hours later; it was supposed to be secret, although Nixon had photographs taken. Krogh came up with talking points like an anti-drug rock musical (seriously) and making anti-drug advertisements.

What Elvis really wanted was the badge. Krogh recounts:

And then the real reason for the trip finally came out as Elvis said, “Mr. President, can you get me a badge from the Bureau of Narcotics and Dangerous Drugs?” And the president looked and he said, “Bud, can we get him a badge?” And I said, “Well, Mr. President, if you want to get him a badge, we can do that.” He said, “Well, get him a badge.”

Elvis ended up hugging Nixon, then asking if his bodyguards could come in. Nixon gave each bodyguards a present out of a drawer, and Elvis -- ever the persuader -- chimed in with "they have wives". Krogh said Nixon "dived back into the drawer again and out come the presents for the wives".

Unfortunately, this happened before Nixon installed his famous tape recorders, so there's no Elvis-Nixon tape; however, the meeting did leak to the press in a story by Jack Anderson not long after the meeting happened.

Krogh called Finlator and told him to make the badge; as reported by the Anderson, that upon receiving it, Elvis was "overcome by emotion".

...

The meeting is now often characterized as a long con by Elvis (although Elvis was probably not "high as a kite" as has sometimes been speculated -- this was a little early in his biography for his more extreme pill-taking, and the Secret Service would likely not have allowed a drugged-out Elvis to get anywhere near the President).

But -- when Elvis said on stage he as a federal narcotics agent -- did he really think he was? I've so far left out a key detail to the story. He also liked to play at being a police officer.

He had a million badges and a blue police light on his car.

That's Priscilla Presley. Elvis would like to put his light on and pull people over, and warn them they were speeding. (This wasn't quite full officer impersonation, since Elvis was definitely recognizable.) He also would listen to the police scanner and when an accident occurred would drive to the scene to direct traffic.

According to two different sources (although admittedly this may be braggadocio from Elvis himself) he once saw two men attacking a man at a gas station, and jumped out of his limo to break up the fight. Everyone stopped fighting (it's Elvis, after all) and they ended up posing for pictures.

As far as being a drug agent goes, Elvis asked his (high-school aged) stepbrothers to report any drug activity, and also used the badge once to stop a plane on a tarmac (Elvis's valet, James Caughley, was missing).

Finlator (the one who gave Presley the badge) called every six months to check to make sure Elvis still had the badge, but nothing came about otherwise -- no anti-drug commercials or rock musical. But all indications are that Elvis thought the Federal Agent title was real, like being a seventh or eighth level black belt, even if he didn't take on any real responsibilities.

...

Carman, W. (1998). Elvis's Karate Legacy. Legacy Entertainment.

Guralnick, P. & Jorgensen, E. (1999). Elvis Day by Day: The Definitive Record of His Life and Music. Ballantine Books.

Krogh, E. (1994). The Day Elvis Met Nixon. Pejam.

Presley, P. & Presley, L. (2005). Elvis by the Presleys. Crown.

Here are some links to a couple posts I've done about music in the past!

How well could the average medieval peasant sing?

Black musical influences on sea shanties

The singing prostitutes of medieval Japan

Work song of Scottish herring gutters

The History of western music from the 10th thru the 16th centuries (often known as “Early Music”)is very interesting, so I’m going to put in some trivia on that.

What was ‘Gregorian chant’?

Recently there was a bit of a fad regarding Gregorian chant. Its calm beauty and sombre solemnity was the source of a number of memes and playlists and compilations came out on music streaming sites. But what exactly is Gregorian chant?

Well, it’s only the source of most of western ideas about counterpoint and tonality.

Let’s start by asking where the type of liturgical chant commonly (and rather falsely) known as “Gregorian” came from. Popular legend claims that a dove perched on the shoulder of Pope Gregory I and dictated to him the entirety of the chant repertory. This legend is thought to have arisen in the 14th century, but nevertheless it is the reason why the chant is called ‘Gregorian’. In reality, the melodic content of the chant was probably not developed during Gregory’s time, and certainly the notation system (the neumatic system ) used for notating chants was not developed yet. It is more accurately called ‘Frankish-Roman’ chant since it came from Carolingian era practices.

Gregorian chant is a monophonic (‘one-voice’ melody) setting parts of Catholic liturgy. A single singer or group of singers in unison would deliver it in a flat, monotone voice without accompaniment. They had simple, clean melodies, but gradually more and more improvised ornamentation came to be added by the singers.

The chant repertory was essential to the development of modes. Modes are patterns of intervals. Theorists in the 10th through 12th centuries divided the chants into eight modes, each with a different starting note and a different organization of pitches. Today, there are only two modes in common use, Major and minor, neither of which corresponds to any of the early church modes. But modes were the beginning of the development of keys and absolutely integral to western tonality.

Later, starting in the 10th century and fully developing by the 12th century, polyphony and counterpoint were introduced by means of what was known as organum. Organum used a pre-existing chant and added other voices to it as accompaniment or texture. There were two schools of thought or methods of organum. The first , Early Organum, placed the original chant on the top voice, and other accompaniment lines below. The second, called Notre Dame School Organum, places the chant in the bottom, or Tenor, voice. A florid accompaniment line is then written on top of it. Over time, Notre Dame Organum became so heavily ornamented that the original chant was no longer recognizable. Together these two schools of organum formed the basis for modern polyphony.

Who was Guido of Arezzo and why is he important?

Guido was the most influential music theorist of the Early Middle Ages, and is credited with the development of an early version of the hexachord (a concept of early tonality that is a predecessor to the modern scale), solfegge symbols (do, re,mi,fa, etc) with a famous memory aide known as the Guidonian Hand, and the notation system that would later become modern staff notation. Basically, he made western tonality as we know it today possible.

Why are the high parts in music from this era usually sung by male singers, and who were the castrati?

It all goes back to the Catholic Church. One of the earliest well-known composers was a woman, Hildregarde of Bingen (c.1098 – 17 September 1179), who wrote primarily for female voices, the nuns in her abbey. There were other instances of female composers and performers in Medieval and Renaissance times. However, a 1588 decree by Pope Sixtus V banned women from singing in any public setting. They were already banned from singing in church by the Pauline dictum “mulieres in ecclesiis tacesant” (“let women keep silent in the church”).

But the high, heavily ornamented soprano parts written by composers of that period needed a voice that was more clear and powerful than that of a countertenor or falsettist (a male singer who uses mainly his head voice to achieve a high vocal range)but more agile, steady and reliable than that of a boy. So Sixtus V published another decree, the bull known as Cum Pro Nostro Pastorali Munere in 1589 allowing for the presence of castrati in church choirs.

The castrati were male singers trained from early childhood who were castrated as young boys to retain their high voices. It’s hard to find information about the exact origin of the castrati, but the custom had begun in Italy about a century earlier. The castrati quickly became wildly popular, as the first operas were written and performed in Italy in the early 1600s. They were celebrated figures and the biggest stars of the music world. The most famous castrato was Carlo Brosci, known as Farinelli. He worked closely with the composers Porpora and Handel. Even after the church’s decree against women singers was lifted, the castrati filled many of the major roles in opera and sung other secular and religious music.

In modern times, the high voices from music from this period are performed by either women or, more recently, countertenors.

here is a pretty good basic video on the topic of countertenors and other high male voices in Early Music.

What influence did Medieval Troubadors have on music?

Troubadours (and their Northern counterparts , Trouveres) active from the 12th-14th centuries, were the first influential secular musicians.

The troubadour songs were usually monophonic melodies sung by a single vocalist, sometimes accompanied by a lute. They were in various genres, mostly describing love and longing. For example, the Canso was a song describing a knight’s love for an idealized, distant lady. The Pastorela was a jovial tale about a knight falling in love with a shepardess. Each genre had its own musical style and form.

The famous Trouvere Adam de La Halle identified three major forms of song, the rondeau, ballade, and virelai, that greatly influenced later forms of music. The rondeau, for example, had two sections of music, a and b, and a refrain which took material from the b section, B. The form was then B-aab-B-aab etc. Similar forms were used heavily throughout the Baroque period and continued to influence musical forms even later.