# Yamaha YM2151 datasheet

## OUTLINE OF FUNCTIONS AND FEATURES

### 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.

### Features

• 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:

$E(t) = A(t)\times \sin[(Nc + Dc) \times wt + B(t) \times \sin(Nm + Dm) \times wt]$

• 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

$\frac{Nc + Dc}{Nm + Dm} = 1$, $B(t) = 0$

Fig. 1.3

$\frac{Nc+ Dc}{Nm+Dm} = 1$, $B(t) = 0.5$

Fig. 1.4

$\frac{Nc+ Dc}{Nm+Dm} = 1$, $B(t) = 1.0$

Fig. 1.5

$\frac{Nc+ Dc}{Nm+Dm} = 1$, $B(t)= 1.5$

Fig. 1.6

$\frac{Nc+ Dc}{Nm+Dm} = 1$, $B(t)= 2.0$

Fig. 1.7

$\frac{Nc+ Dc}{Nm+Dm} = 0.5$, $B(t)= 0.5$

Fig. 1.8

$\frac{Nc+ Dc}{Nm+Dm} = 0.5$, $B(t) = 1.0$

Fig. 1.9

$\frac{Nc+ Dc}{Nm+Dm} = 0.5$, $B(t)= 1.5$

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

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

Fig. 1.11

Example output of a-point waveform.