音频界的瑞士军刀 --- SoX - Sound eXchange 国外开源音频处理软件介绍

今天我给大家介绍一款自称是音频处理界的瑞士军刀的一款开源软件，SoX - Sound eXchange。引用主页上介绍的原话：

        Welcome to the home of SoX, the Swiss Army knife of sound processing programs.

该软件的主页是http://sox.sourceforge.net/，文章介绍不详细的地方大家可以翻阅其主页。

        SoX是一个跨平台(Windows, Linux, MacOS X, etc.)命令行程序，用于各种格式的转换，播放和各种音频格式，以及给音频加入特效。 下图是一个运行的实例。



接下来，到了解剖这个瑞士军刀的时候了！

一、软件支持各种常见的音频格式，这也是该软件的一大卖点。

Raw files in various binary formats Raw textual data Amiga 8svx files Apple/SGI AIFF files SUN .au files PCM, u-law, A-law G7xx ADPCM files (read only) mutant DEC .au files NeXT .snd files AVR files CDDA (Compact Disc Digital Audio format) CVS and VMS files (continuous variable slope) Grandstream ring-tone files GSM files HTK files LPC-10 files Macintosh HCOM files Amiga MAUD files AMR-WB & AMR-NB (with optional libamrwb & libamrnb libraries) MP2/MP3 (with optional libmad, libtwolame and libmp3lame libraries) MP4, AAC, AC3, WAVPACK, AMR-NB files (with optional ffmpeg library) AVI, WMV, Ogg Theora, MPEG video files (with optional ffmpeg library)

Ogg Vorbis files (with optional Ogg Vorbis libraries) FLAC files (with optional libFLAC) IRCAM SoundFile files NIST SPHERE files Turtle beach SampleVision files Sounder & Soundtool (DOS) files Yamaha TX-16W sampler files SoundBlaster .VOC files Dialogic/OKI ADPCM files (.VOX) Microsoft .WAV files PCM, floating point u-law, A-law, MS ADPCM, IMA (DMI) ADPCM GSM RIFX (big endian) WavPack files (with optional libwavpack library) Psion (palmtop) A-law WVE files and Record voice notes Maxis XA Audio files EA ADPCM (read support only, for now) Pseudo formats that allow direct playing/recording from most audio devices The "null" pseudo-file that reads and writes from/to nowhere

二、常见的音效和音频处理

音调/滤波特效
全通: RBJ all-pass biquad IIR filter
带通: RBJ band-pass biquad IIR filter
带阻: RBJ band-reject biquad IIR filter
通带: SPKit resonator band-pass IIR filter
低音: Tone control: RBJ shelving biquad IIR filter
高音: Tone control: RBJ shelving biquad IIR filter
均衡: RBJ peaking equalisation biquad IIR filter
FFTFIR滤波: FFT convolution FIR filter using given freq. response (W.I.P.)
高通: High-pass filter: Single pole or RBJ biquad IIR
希尔伯特滤波器: Hilbert transform filter (90 degrees phase shift)
低通: Low-pass filter: single pole or RBJ biquad IIR
sinc滤波器: Sinc-windowed low/high-pass/band-pass/reject FIR

附加特效
合唱: Make a single instrument sound like many
延时: Delay one or more channels
回声: Add an echo
多回声: Add a sequence of echos
法兰效应: Stereo flanger
过载: Non-linear distortion
相移: Phase shifter
重复: Loop the audio a number of times
混响: Add reverberation
翻转: Reverse the audio (to search for Satanic messages ;-)
颤音: Sinusoidal volume modulation

音量幅度特效
幅度变化: Signal level compression/expansion/limiting
对比化: Phase contrast volume enhancement
去直流: Apply or remove DC offset
淡入淡出: Apply a fade-in and/or fade-out to the audio
增益变化: Apply gain or attenuation; normalise/equalise/balance/headroom
响度控制: Gain control with ISO 226 loudness compensation
多带幅度变化: Multi-band compression/expansion/limiting
归一化: Normalise to 0dB (or other)
音量调节: Adjust audio volume

编辑特效
拉长: Pad (usually) the ends of the audio with silence
去除静音: Remove portions of silence from the audio
结合: Perform the equivalent of a cross-faded tape splice
裁剪: Cuts portions out of the audio
VAD: Voice activity detector

混音特效
声道混音: Auto mix or duplicate to change number of channels
分声道: Divide sample values by those in the 1st channel (W.I.P.)
任意输出混音: Produce arbitrarily mixed output channels
翻转声道: Swap stereo channels

音调节拍特效
弯曲声调: Bend pitch at given times without changing tempo
变调: Adjust pitch (= key) without changing tempo
变速: Adjust pitch & tempo together
拉伸压缩: Adjust tempo without changing pitch (simple alg.)
变节拍: Adjust tempo without changing pitch (WSOLA alg.)

高级特效
加入噪声: Add dither noise to increase quantisation SNR
重采样: Change audio sampling rate

特殊滤波器和混音器
去加重: ISO 908 CD de-emphasis (shelving) IIR filter
耳机增强: Process CD audio to best effect for headphone use
去噪声: Filter out noise from the audio
卡拉ok效应: Out Of Phase Stereo (or `Karaoke') effect
RIAA: RIAA vinyl playback equalisation

分析
噪声分析: Produce a DFT profile of the audio (use with noisered)
频谱分析: graph signal level vs. frequency & time (needs `libpng')
状态分析: Enumerate audio peak & RMS levels, approx. freq., etc.
多声道状态: Multichannel aware `stat'

多方面效应
LADSPA : Apply LADSPA plug-in effects e.g. CMT (Computer Music Toolkit)
合成声音: Synthesise/modulate audio tones or noise signals
新文件: Create a new output file when an effects chain ends.
重试: Restart 1st effects chain when multiple chains exist.

低音量处理特效
滤波: 2nd-order IIR filter using externally provided coefficients
降采样: Reduce sample rate by discarding samples
fir滤波: FFT convolution FIR filter using externally provided coefficients
升采样: Increase sample rate by zero stuffing