数字音频处理的瑞士军刀sox的音效算法以及用法

　　SoX可以明确的写出需要的音频处理的效果，可以方便的重复使用，在目前的条件下是一个比较方便使用的项目。不过相信随着Audacity的发展，很有可能在未来可以逐渐替代SoX的功能。

对于SoX主要关心的是她的音频效果功能，因为文件格式转换，播放，录音功能在ffmpeg中已经更大程度上的得到实现了。SoX的效果列表如下：

Tone/filter effects [滤波器啦]

allpass: RBJ all-pass biquad IIR filter
bandpass: RBJ band-pass biquad IIR filter
bandreject: RBJ band-reject biquad IIR filter
band: SPKit resonator band-pass IIR filter
bass: Tone control: RBJ shelving biquad IIR filter
equalizer: RBJ peaking equalisation biquad IIR filter
firfit+: FFT convolution FIR filter using given freq. response (W.I.P.)
highpass: High-pass filter: Single pole or RBJ biquad IIR
hilbert: Hilbert transform filter (90 degrees phase shift)
lowpass: Low-pass filter: single pole or RBJ biquad IIR
sinc: Sinc-windowed low/high-pass/band-pass/reject FIR
treble: Tone control: RBJ shelving biquad IIR filter

example：

1 play file.wav bass -20
2 play file.wav bass +20

Production effects [合成效果]

chorus: Make a single instrument sound like many
delay: Delay one or more channels
echo: Add an echo
echos: Add a sequence of echos
flanger: Stereo flanger
overdrive: Non-linear distortion
phaser: Phase shifter
repeat: Loop the audio a number of times
reverb: Add reverberation
reverse: Reverse the audio (to search for Satanic messages ;-)
tremolo: Sinusoidal volume modulation

example：
1 play file.wav tremolo 3.5 60 //颤抖音效果
2 play file.xxx echo 0.8 0.88 60 0.4 //回音效果

Volume/level effects [音量效果]

compand: Signal level compression/expansion/limiting
contrast: Phase contrast volume enhancement
dcshift: Apply or remove DC offset
fade: Apply a fade-in and/or fade-out to the audio
gain: Apply gain or attenuation; normalise/equalise/balance/headroom
loudness: Gain control with ISO 226 loudness compensation
mcompand: Multi-band compression/expansion/limiting
norm: Normalise to 0dB (or other)
vol: Adjust audio volume

examle：
1 play *.wav fade t 00:00:50.09 00:01:00 00:00:06 //设置淡入淡出效果

Editing effects [音频编辑效果，主要是添加、删除一类的功能]

pad: Pad (usually) the ends of the audio with silence
silence: Remove portions of silence from the audio
splice: Perform the equivalent of a cross-faded tape splice
trim: Cuts portions out of the audio
vad: Voice activity detector

Mixing effects [混音效果]

channels: Auto mix or duplicate to change number of channels
divide+: Divide sample values by those in the 1st channel (W.I.P.)
remix: Produce arbitrarily mixed output channels
swap: Swap stereo channels

Pitch/tempo effects [节奏和音高的功能，pitch 就是那个传说中调音高的算法了]

bend: Bend pitch at given times without changing tempo
pitch: Adjust pitch (= key) without changing tempo
speed: Adjust pitch & tempo together
stretch: Adjust tempo without changing pitch (simple alg.)
tempo: Adjust tempo without changing pitch (WSOLA alg.)

example：
1 sox file1.wav file2.wav speed 1.29

Mastering effects [这个不知道是啥意思，就下面两个效果，一个是添加抖动来提升信噪比的，一个效果采样率的。第一个效果不错]

dither: Add dither noise to increase quantisation SNR
rate: Change audio sampling rate

example：
1 play file.wav dither 100 

Specialised filters/mixers [比较奇怪的效果]

deemph: ISO 908 CD de-emphasis (shelving) IIR filter
earwax: Process CD audio to best effect for headphone use
noisered: Filter out noise from the audio
oops: Out Of Phase Stereo (or `Karaoke`) effect
riaa: RIAA vinyl playback equalisation

Analysis effects [用来显示统计信息的功能]

noiseprof: Produce a DFT profile of the audio (use with noisered)
spectrogram: graph signal level vs. frequency & time (needs `libpng`)
stat: Enumerate audio peak & RMS levels, approx. freq., etc.
stats: Multichannel aware `stat`

example：
1 sox 杨望.wav -n stat //统计信息

Miscellaneous effects [附加功能， 比较有意思]

ladspa: Apply LADSPA plug-in effects e.g. CMT (Computer Music Toolkit)
synth: Synthesise/modulate audio tones or noise signals
newfile: Create a new output file when an effects chain ends.
restart: Restart 1st effects chain when multiple chains exist.

Low-level signal processing effects [底层的处理功能，感觉和滤波器那组比较像啦]

biquad: 2nd-order IIR filter using externally provided coefficients
downsample: Reduce sample rate by discarding samples
fir: FFT convolution FIR filter using externally provided coefficients
upsample: Increase sample rate by zero stuffing

参考网址： https://linux.die.net/man/1/soxexam