# Yamaha YM2151 datasheet

## Contents

## 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:

<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>

**Fig. 1.3**

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

**Fig. 1.4**

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

**Fig. 1.5**

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

**Fig. 1.6**

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

**Fig. 1.7**

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

**Fig. 1.8**

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

**Fig. 1.9**

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

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.