數字音頻處理的瑞士軍刀sox的音效演算法以及用法

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　　SoX可以明確的寫出需要的音頻處理的效果，可以方便的重複使用，在目前的條件下是一個比較方便使用的項目。不過相信隨著Audacity的發展，很有可能在未來可以逐漸替代SoX的功能。

對於SoX主要關心的是她的音頻效果功能，因為檔案格式轉換，播放，錄音功能在ffmpeg中已經更大程度上的得到實現了。SoX的效果列表如下：

Tone/filter effects [濾波器啦]

allpass: RBJ all-pass biquad IIR filterbandpass: RBJ band-pass biquad IIR filterbandreject: RBJ band-reject biquad IIR filterband: SPKit resonator band-pass IIR filterbass: Tone control: RBJ shelving biquad IIR filterequalizer: RBJ peaking equalisation biquad IIR filterfirfit+: FFT convolution FIR filter using given freq. response (W.I.P.)highpass: High-pass filter: Single pole or RBJ biquad IIRhilbert: Hilbert transform filter (90 degrees phase shift)lowpass: Low-pass filter: single pole or RBJ biquad IIRsinc: Sinc-windowed low/high-pass/band-pass/reject FIRtreble: 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 manydelay: Delay one or more channelsecho: Add an echoechos: Add a sequence of echosflanger: Stereo flangeroverdrive: Non-linear distortionphaser: Phase shifterrepeat: Loop the audio a number of timesreverb: Add reverberationreverse: Reverse the audio (to search for Satanic messages ;-)tremolo: Sinusoidal volume modulation

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

Volume/level effects [音量效果]

compand: Signal level compression/expansion/limitingcontrast: Phase contrast volume enhancementdcshift: Apply or remove DC offsetfade: Apply a fade-in and/or fade-out to the audiogain: Apply gain or attenuation; normalise/equalise/balance/headroomloudness: Gain control with ISO 226 loudness compensationmcompand: 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 //設定淡入淡出效果

Editing effects [音頻編輯效果，主要是添加、刪除一類的功能]

pad: Pad (usually) the ends of the audio with silencesilence: Remove portions of silence from the audiosplice: Perform the equivalent of a cross-faded tape splicetrim: Cuts portions out of the audiovad: Voice activity detector

Mixing effects [混音效果]

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

Pitch/tempo effects [節奏和音高的功能，pitch 就是那個傳說中調音高的演算法了]

bend: Bend pitch at given times without changing tempopitch: Adjust pitch (= key) without changing tempospeed: Adjust pitch & tempo togetherstretch: 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 [這個不知道是啥意思，就下面兩個效果，一個是添加抖動來提升信噪比的，一個效果採樣率的。第一個效果不錯]

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

example：
1 play file.wav dither 100 

Specialised filters/mixers [比較奇怪的效果]

deemph: ISO 908 CD de-emphasis (shelving) IIR filterearwax: Process CD audio to best effect for headphone usenoisered: Filter out noise from the audiooops: Out Of Phase Stereo (or `Karaoke`) effectriaa: RIAA vinyl playback equalisation

Analysis effects [用來顯示統計資訊的功能]

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 楊望.wav -n stat //統計資訊

Miscellaneous effects [附加功能， 比較有意思]

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

Low-level signal processing effects [底層的處理功能，感覺和濾波器那組比較像啦]

biquad: 2nd-order IIR filter using externally provided coefficientsdownsample: Reduce sample rate by discarding samplesfir: FFT convolution FIR filter using externally provided coefficientsupsample: Increase sample rate by zero stuffing

數字音頻處理的瑞士軍刀sox的音效演算法以及用法