Sound Synthesis

声音合成

Periodic electric signals can be converted into sound by amplifying them and driving a loudspeaker with them. One way to do this is to simply add various amplitudes of the harmonics of a chosen pitch until the desired timbre is obtained, called additive synthesis. Another way is to start with geometric waves, which are rich in harmonic content, and filter the harmonics to produce a new sound- subtractive synthesis.

周期性电信号可以通过放大并用它们驱动扬声器将其转换为声音。一种方法是 simply 添加所选音调的各种谐波幅度，直到获得所需的音色，这称为加法合成。另一种方法是从具有丰富谐波内容的几何波开始，并通过滤波谐波来产生新声音，这称为减法合成。

Modern sound synthesis makes increasing use of MIDI for sequencing and communication between devices.

现代声音合成越来越多地使用MIDI进行序列生成和设备间的通信。

Methods of Synthesis

合成方法

Jeff Pressing in "Synthesizer Performance and Real-Time Techniques" gives this list of approaches to sound synthesis.

杰弗·普雷斯廷在《合成器表现与实时技术》中给出了以下几种声音合成方法。

additive synthesis - combining tones, typically harmonics of varying amplitudes

加法合成 - 将不同振幅的谐波组合在一起

subtractive synthesis - filtering of complex sounds to shape harmonic spectrum, typically starting with geometric waves.

减法合成 - 通过过滤复杂声音来塑造谐波谱，通常从几何波开始。

frequency modulation synthesis - modulating a carrier wave with one or more operators

频率调制合成 - 用一个或多个运算符调制载波波形

sampling - using recorded sounds as sound sources subject to modification

采样 - 使用录音声音作为声音源并进行修改

composite synthesis - using artificial and sampled sounds to establish resultant "new" sound

复合合成 - 使用人工和采样声音来产生“新的”声音

phase distortion - altering speed of waveforms stored in wavetables during playback

相位失真 - 在播放存储在波表中的波形时改变波形的速率

waveshaping - intentional distortion of a signal to produce a modified result

波形变换 - 故意对信号进行扭曲以产生修改后的结果

resynthesis - modification of digitally sampled sounds before playback

重采样 - 在播放前对数字采样声音进行修改

granular synthesis - combining of several small sound segments into a new sound

颗粒合成 - 将多个小声音片段组合成新的声音

linear predictive coding - technique for speech synthesis

线性预测编码 - 一种用于语音合成的技术

direct digital synthesis - computer modification of generated waveforms

直接数字合成 - 计算机对生成波形的修改

wave sequencing - linear combinations of severtal small segments to create a new sound

波形序列 - 由多个小段的线性组合生成新的声音

vector synthesis - technique for fading between any number of different sound sources

矢量合成 - 一种在不同声音源之间渐变的技术

physical modeling - mathematical equations of acoustic characteristics of sound

物理建模 - 声音的声学特性的数学方程

MIDI for Music

MIDI 用于音乐

Musical Instrument Digital Interface (MIDI) is a data transfer protocol which is widely used with music synthesizers. MIDI can be used as a controller between modules in an integrated music system. It uses a serial data connection with five leads. It uses two basic message types - channel and system. Channel messages can be sent from machine to machine over any one of 16 channels to control an instrument's voice parameters or to control the way the instrument responds to voice messages. System messages can be directed to all devices in the system (called "common" messages) or can be directed to a specific machine (exclusive). Within the MIDI protocol, a basic set of standards has been developed called the General MIDI specification, or just GM. It attempts to standardize common practices within MIDI and make it more accessible to the general user. GM is particularly appropriate for a personal computer-based MIDI system using a sound card in the computer. Part of the GM standard requires support for a basic set of 128 instruments, a minimum of 24-voice polyphony, and polytimbrality to at least 16 sounds deep.

MIDI（音乐乐器数字接口）是一种广泛用于音乐合成器的数据传输协议。MIDI可以作为集成音乐系统中模块之间的控制器。它使用五根引线的串行数据连接。它使用两种基本消息类型——通道消息和系统消息。通道消息可以经由16个通道中的任何一个从一台机器发送到另一台机器，以控制乐器的音色参数或控制乐器对音色消息的响应方式。系统消息可以发送到系统中的所有设备（称为“通用”消息），也可以发送到特定的设备（独占）。在MIDI协议中，制定了一套基本标准，称为通用MIDI规范，或简称GM。它试图标准化MIDI中的常见做法，并使其更易于一般用户使用。GM特别适用于基于个人计算机的MIDI系统，该系统使用计算机中的声卡。GM标准的一部分要求支持基本的128种乐器，至少24个音轨的多音色能力，并且多音色能力至少支持16种声音。

Using a MIDI sequencer to control one or more instruments has some significant practical benefits. A MIDI sequence which plays several minutes of music can be stored in a few kilobytes of memory on a computer, whereas the storage of a minute's worth of digitally precise and clear CD quality music directly on a computer disc might take 10 MB of memory. The MIDI file is just a digital representation of the sequence of notes with information about pitch, duration, voice, etc., and that takes much less memory than the digitally recorded image of the complex sound.

使用MIDI序列器控制一个或多个乐器有一些重要的实际好处。一个播放几分钟音乐的MIDI序列可以存储在计算机的几千字节内存中，而将一分钟的高质量数字音乐直接存储在计算机磁盘上可能需要10 MB的内存。MIDI文件只是对音符序列的数字表示，包含有关音调、持续时间、声部等的信息，其占用的内存远少于对复杂声音的数字记录。

Other practical benefits include the ability to transpose music without changing its duration, to change its tempo without changing its pitch, or change the synthetic instruments used to perform the piece of music. Drawbacks include the inability to easily include a recorded voice part or played instrument along with the MIDI sequenced sound, but on the other hand, the music can be easily synchronized with multimedia events in a production.

其他实际好处包括能够不改变持续时间地转调音乐，不改变音调地改变节奏，或更换用于演奏音乐的合成乐器。缺点是难以方便地加入录制的声部或演奏的乐器，但另一方面，音乐可以很容易地与多媒体事件在制作中同步。