In the U.S., sheet music became highly popular early in the twentieth century. Tin Pan Alley in New York City, as well as less famous song publishers in Chicago, led publication of about 30 million copies of sheet music in 1910. By 1918, Woolworth’s Five and Dime stores alone were selling 200 million copies of sheet music at a dime each. Hit songs sold millions of copies of sheet music: top sellers were Whiting and Egan’s “Till We Meet Again” (1918), 3.5 million copies; Kendis-Brockman’s “I’m Forever Blowing Bubbles” (1919), 2.6 million copies; and Alfred Bryan’s “Joan of Arc” (1917), more than 2 million copies. At least five other songs also sold a million or more copies of sheet music.
Prior to roughly 1890, print music was the only feasible way to distribute widely music. Before then, almost no one had heard any music other than live music. The ability to read and accurately understand verbal texts requires much time and effort in specific education. The ability to read and accurately recreate music from a musical text also requires much time and effort in specific education. However, the later investment has narrower value and depends on less universally distributed natural skills. The development of mechanical reproduction of music greatly lowered the total cost of high quality, mass access to the sound of authored musical works.
Print music peaked relative to other print revenue about 1919, well after the development of media for the mechanical reproduction of music. Sheet music output grew tremendously from 1890 to 1919. Media and machines for the mechanical reproduction of music also grew strongly from the end of the nineteenth century to 1919. In 1919, 107 million recorded disks and cylinders were produced. In 1919, 54% of pianos produced were mechanically powered (self-playing). The nominal price of sheet music was much cheaper than that of recorded music and player pianos. The nominal price of sheet music, of course, does not include the cost of learning to read it and to make high-fidelity music from it. On the other hand, anyone can try to sing and may well enjoy the activity even without high-quality results. Moreover, sheet music included visually attractive covers and probably was an object of common discussion. Sheet music revenue actually rose relative to recordings revenue across the 1920s. Increasing general interest in music, along with wealth and media-nominal-cost disparities, probably accounts for sheet music increasing in popularity along with the early development of mechanical reproduction of music.
Despite large declines in the real cost of recorded music, U.S. music industry print revenue relative to newspaper, periodical, and book industries print revenue has been surprisingly large in recent years. In 1890, when almost no one had access to mechanically reproduced music, print music industry revenue (sheet music and music books sold at wholesale) was 0.8% of newspaper, periodical, and book (wholesale book publishing) industries revenue. This figure rose to 1.5% in 1919. In 2007, sheet music and music books generated $1.7 billion in wholesale revenue. That amount is 1.7% of newspaper, periodical, and book print revenue. Print music today plays no part in popular culture, but, relative to other print, it generates revenue comparable to that in the late nineteenth and early twentieth centuries.
Why has print music revenue grown along with newspaper, periodical, and book print revenue? Who buys print music today? Education may be key to the answer. Music instruction is now common in elementary and high-school education. Elementary and high-school education is now universal. Much print music is probably bought for elementary and high-school musical education. Moreover, the market for selling print music to schools is probably less competitive than the retail market for sheet music early in the twentieth century. A less competitive market implies higher prices. Growth in formal musical education may have helped to sustain revenue for the print music business.
Print music today is a totally different social object than it was early in the twentieth century. Early in the twentieth century, a larger share of persons probably had fun looking at print music and making music from it.
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 Sanjek (1996) pp. 32, 34; Goldberg (1930) pp. 218-9.
 On sheet music sales, see first paragraph above, and sheet music sales figures in the 1889-1935 datasheet. The best-selling sheet music from 1902 to 1907 sold about 700,000 copies. See Goldberg (1930) p. 219. Sales by media for four Irving Berlin hit songs suggests a declining share of sheet music sales relative to recordings from 1919 to 1921. Other evidence also suggests increasing importance of disk recordings. In 1919, a recording of the song “Dardanella” sold almost a million copies, while the leading song in the following year, “Whispering”, sold over two million recordings. See Tawa (2005) p. 23. In addition, radio broadcasting began with broadcasting music in 1920. The share of households owning a radio grew strongly across the 1920s to reach 39% in 1930. After 1929, both sheet music and recorded music wholesale revenue dropped sharply.
 For the relevant data, see the print ratio datasheets. Data for 2002 to 2004 indicates a music print ratio of 0.7%. The problem appears to be definitional. Data based on the 1997 NAICS shows $662 million in print music revenue in 2004, while data based on the 2002 NAICS shows $1,591 in print music revenue in that same year. I’d guess that the 2002 NAICS figure is likely to be more accurate. But even a music print ratio of 0.7% is comparable with the music print ratio in 1890, before popular use of media for mechanical reproduction of music.
Galbi, Douglas (2009), Music Media and Print Media in the U.S. from 1889 to 2007, also available as OpenOffice.org Calc spreadsheets)
Goldberg, Isaac (1930), Tin pan alley: a chronicle of the American popular music racket (New York: The John Day Company).
Sanjek, Russell, updated by David Sanjek (1996), Pennies from heaven: the American popular music business in the twentieth century (New York: Da Capo Press).
Tawa, Nicholas (2005), Supremely American: popular song in the 20th century (Lanham, Md.: Scarecrow Press).