AM & Ringmodulation: Introduction

Henrik von Coler

Amplitude modulation (AM) and Ringmodulation are essentially the same technique, yet with a slight variation. Both perform the same operation - modulate the amplitude of a signal - the carrier $c(t)$ - with a modulator $m(t)$:

$$ y(t) = c(t) \cdot m(t) $$

Amplitude Modulation (AM)

Amplitude Modulation was first used for voice transmission by Reginald Fessenden in 1906 (Marconi, 2007). The first commercial radio station KDKA (Pittsburgh), used AM to broadcast news and entertainment in 1920 (Langer, 2015)). In radio transmission, carrier frequencies range from 530 - 1700 kHz. In short-wave AM, the carriers have frequencies of 3 - 30 MHz, allowing for long-range transmission.

Since AM is a method to create overtones with few operators, it was discovered as a tool for manipulating and generating sounds in music. To to that, the carrier frequencies are shifted to the audible range. This creates tremolo effects at low frequencies and so called sidebands at higher frequencies. This creates the typical ringing sound associated with AM.

Karlheinz Stockhausen - Telemusik (1966)

Stockhausen used the AM technique in electronic compositions to create unique spectral textures (Stockhausen, 1966). In Telemusik he creates rapid modulations and layered frequency shifts with AM, espacially audible in the first minute of the piece:

Ring Modulation

Ringmodulation is an audio effect used since the early days of analog sound synthesis and electronic music. Like AM, it has its origins in signal transmission. Ringmodulation is a type of amplitude modulation where both the carrier and modulator are bipolar signals, creating new non-harmonic frequencies, aka sidebands. Similar to AM, ringmodulation cen be used to create metallic sounds.

Karlheinz Stockhausen - Mixtur (1964)

Karlheinz Stockhausen used the ringmodulator in various works as an instrument, as for example in Mixtur (1964):

Morton Subotnick - Silver Apples of the Moon (1967)

One of the first electronic compositions to use ring modulation extensively is Morton Subutnik's Silver Apples of the Moon. Especially in 0:00 - 1:00, the shimmering, bell-like tones and rapidly shifting frequencies are created with ring modulation:

Autechre - Gantz Graf (2002)

Autechre frequently use ring modulation in their pieces (Young, 2018) to create complex, glitchy sounds. In this example, it is used for the metallic textures throughout the piece, especially audible in 0:30 - 2:00:

References

2018

Rob Young. Warped Space: The Autechre Chronicles. MIT Press, 2018. URL: https://mitpress.mit.edu/.
[details] [BibTeX▼]

@book{young2018,
    author = "Young, Rob",
    title = "Warped Space: The Autechre Chronicles",
    publisher = "MIT Press",
    year = "2018",
    url = "https://mitpress.mit.edu/"
}

2015

John W. Langer and Robert D. Burnett. The birth of am radio broadcasting in the 1920s. Radio History Journal, 12(3):45–56, 2015. Accessed: 2025-04-01.
[details] [BibTeX▼]

@article{history_1920s,
    author = "Langer, John W. and Burnett, Robert D.",
    title = "The Birth of AM Radio Broadcasting in the 1920s",
    year = "2015",
    journal = "Radio History Journal",
    volume = "12",
    number = "3",
    pages = "45-56",
    note = "Accessed: 2025-04-01"
}

2007

Guglielmo Marconi and Reginald Fessenden. Reginald Fessenden and the Birth of AM Radio. Prentice Hall, New York, 2007. Accessed: 2025-04-01.
[details] [BibTeX▼]

@book{fessenden_1906,
    author = "Marconi, Guglielmo and Fessenden, Reginald",
    title = "Reginald Fessenden and the Birth of AM Radio",
    year = "2007",
    publisher = "Prentice Hall",
    address = "New York",
    note = "Accessed: 2025-04-01"
}

2001

Curtis Roads. Microsound. MIT Press, 2001. URL: https://mitpress.mit.edu/9780262681544/microsound/.
[details] [BibTeX▼]

@book{roads2001,
    author = "Roads, Curtis",
    title = "Microsound",
    publisher = "MIT Press",
    year = "2001",
    url = "https://mitpress.mit.edu/9780262681544/microsound/"
}

1988

F. Richard Moore. Elements of Computer Music. Prentice Hall, 1988. URL: https://www.worldcat.org/title/19129882.
[details] [BibTeX▼]

@book{moore1988,
    author = "Moore, F. Richard",
    title = "Elements of Computer Music",
    publisher = "Prentice Hall",
    year = "1988",
    url = "https://www.worldcat.org/title/19129882"
}

1966

Karlheinz Stockhausen. Telemusik. Elektronische Musik, 1966. URL: https://www.stockhausenmusic.com/.
[details] [BibTeX▼]

@book{stockhausen1966,
    author = "Stockhausen, Karlheinz",
    title = "Telemusik",
    publisher = "Elektronische Musik",
    year = "1966",
    url = "https://www.stockhausenmusic.com/"
}