Yamaha YM2151 datasheet

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Outline of Functions

The YM2151 is an FM-type sound generator equipped with an 8 bit bus line and capable of producing superb audio quality via a microprocessor program. When this IC is used in tandem with the specially-developed YM3012 D/A converter. you can obtain 8-note, left-right/2 channel audio signals. In addition, this unit is equipped with noise, vibrato, an amplitude modulation circuit, a sound effects circuit. and timer. The package is a 24-pin dual in-line package.


  • Generate up to 8 notes.
  • Generate noise.
  • Timbre can be altered temporally.
  • High harmonic can be de-harmonized from the base frequency.
  • De-harmonize between octaves.
  • Interval settings of up to 1.6 cents.
  • Add vibrato and amplitude modulation.
  • Generate a variety of sound effects by extreme de-harmonization of the high harmonic from the base frequency and massive vibrato and amplitude modulation.

Summary of the Principles of FM-type Sound Generation

FM-type sound can be expressed via a basic configuration like that depicted in Figure 1.1. If this were to be expressed formally. it would look like this:

Fig 1-1.PNG

<math>E(t) = A(t)\times \sin[(Nc + Dc) \times wt + B(t) \times \sin(Nm + Dm) \times wt]</math>

  • A(t) : Volume envelope
  • B(t) : Timbre envelope
  • Nx : 1/2 of the basic pitch or multiple value
  • Dx : 1/2 of the basic pitch (1.6 cents) harmonic value

For example, when B(t) = 0, you get a sine wave of (No + Dc) times with respect to the basic pitch. In this case, if we assume values for Nc and Dc like those given above, we will obtain a 1/2 the basic pitch or a sine wave of multiple value. As long as the value for De is not 0, the output will indicate a pitch sine wave slightly offset from 1/2 the basic pitch or multiple value. When B(t) is greater than 0, the output will not be a sine wave but a wave form including a high harmonic component, because B(t) * sin (Nm + Dm) * wt is added onto the (Nc + Dc) * wt phase information. It therefore follows that a variety of wave forms including a high harmonic component can be obtained by selecting different values for B(t) and (Nm + Dm). Also, the timbre can be altered and output by temporal adjustment of B(t).

Actual output patterns when altering the value of B(t) and (Nm + Dm) and adding it onto the previous pattern arc indicated in Fig. 1.2-1.9.

Fig. 1.2

<math>\frac{Nc + Dc}{Nm + Dm} = 1</math>, <math>B(t) = 0</math>

Ym2151 Picture2.jpg

Fig. 1.3

<math>\frac{Nc+ Dc}{Nm+Dm} = 1</math>, <math>B(t) = 0.5</math>

Ym2151 Picture3.jpg

Fig. 1.4

<math>\frac{Nc+ Dc}{Nm+Dm} = 1</math>, <math>B(t) = 1.0</math>

Ym2151 Picture4.jpg

Fig. 1.5

<math>\frac{Nc+ Dc}{Nm+Dm} = 1</math>, <math>B(t)= 1.5</math>

Ym2151 Picture5.jpg

Fig. 1.6

<math>\frac{Nc+ Dc}{Nm+Dm} = 1</math>, <math>B(t)= 2.0</math>

Ym2151 Picture6.jpg

Fig. 1.7

<math>\frac{Nc+ Dc}{Nm+Dm} = 0.5</math>, <math>B(t)= 0.5</math>

Ym2151 Picture7.jpg

Fig. 1.8

<math>\frac{Nc+ Dc}{Nm+Dm} = 0.5</math>, <math>B(t) = 1.0</math>

Ym2151 Picture8.jpg

Fig. 1.9

<math>\frac{Nc+ Dc}{Nm+Dm} = 0.5</math>, <math>B(t)= 1.5</math>

Ym2151 Picture9.jpg

The YM2151 is equipped to handle 7 different kinds of combinatory connection methods. with two circuits composed of this basic structure assigned to a single note, which can be arranged serially or in parallel, or made to act as only a sine- wave sound source. In addition, with the unit set up as in Figure 1.10, with inclusion of a circuit that takes one's own output signal and returns it to oneself, virtually any type of wave form can be obtained via proper adjustment

Fig. 1.10

Fig 1-10.png

An example of the wave form in this case is depicted in Figure 1.11

Fig. 1.11

Example output of a-point waveform.

Ym2151 Picture11.jpg