soxexam.txt

visual c++编写关于声音分析的 傅立叶变换．超牛

       The sample will be bounced twice in asymmetric echos:

	     play file.xxx echos 0.8 0.7 700.0 0.25 900.0 0.3

       The sample will sound as if played in a garage:

	     play file.xxx echos 0.8 0.7 40.0 0.25 63.0 0.3

       Chorus

       The chorus effect has its name because it will often be used to make  a
       single  vocal  sound  like  a  chorus.  But  it can be applied to other
       instrument samples too.

       It works like the echo effect with a short delay, but the  delay	 isn’t
       constant.  The delay is varied using a sinusoidal or triangular modula-
       tion. The modulation depth defines the range  the  modulated  delay  is
       played  before  or  after the delay. Hence the delayed sound will sound
       slower or faster, that is the delayed sound tuned around	 the  original
       one, like in a chorus where some vocals are a bit out of tune.

       The  typical  delay is around 40ms to 60ms, the speed of the modulation
       is best near 0.25Hz and the modulation depth around 2ms.

       A single delay will make the sample more overloaded:

	     play file.xxx chorus 0.7 0.9 55.0 0.4 0.25 2.0 -t

       Two delays of the original samples sound like this:

	     play file.xxx chorus 0.6 0.9 50.0 0.4 0.25 2.0 -t 60.0  0.32  0.4
       1.3 -s

       A big chorus of the sample is (three additional samples):

	      play  file.xxx chorus 0.5 0.9 50.0 0.4 0.25 2.0 -t 60.0 0.32 0.4
       2.3 -t	      40.0 0.3 0.3 1.3 -s

       Flanger

       The flanger effect is like the chorus  effect,  but  the	 delay	varies
       between	0ms  and  maximal  5ms.	 It sound like wind blowing, sometimes
       faster or slower including changes of the speed.

       The flanger effect is widely used in funk and  soul  music,  where  the
       guitar sound varies frequently slow or a bit faster.

       The  typical delay is around 3ms to 5ms, the speed of the modulation is
       best near 0.5Hz.

       Now, let’s groove the sample:

	     play file.xxx flanger 0.6 0.87 3.0 0.9 0.5 -s

       listen carefully between the difference of  sinusoidal  and  triangular
       modulation:

	     play file.xxx flanger 0.6 0.87 3.0 0.9 0.5 -t

       If the decay is a bit lower, than the effect sounds more popular:

	     play file.xxx flanger 0.8 0.88 3.0 0.4 0.5 -t

       The drunken loudspeaker system:

	     play file.xxx flanger 0.9 0.9 4.0 0.23 1.3 -s

       Reverb

       The  reverb effect is often used in audience hall which are to small or
       contain too many many visitors which disturb (dampen) the reflection of
       sound  at  the walls.  Reverb will make the sound be perceived as if it
       were in a large hall.  You can try the reverb effect in	your  bathroom
       or  garage  or sport halls by shouting loud some words. You’ll hear the
       words reflected from the walls.

       The biggest problem in using the reverb effect is the  correct  setting
       of the (wall) delays such that the sound is realistic and doesn’t sound
       like music playing in a	tin  can  or  has  overloaded  feedback	 which
       destroys	 any  illusion	of  playing in a big hall.  To help you obtain
       realistic reverb effects, you should decide first how long  the	reverb
       should  take place until it is not loud enough to be registered by your
       ears. This is be done by varying the  reverb  time  "t".	  To  simulate
       small halls, use 200ms.	To simulate large halls, use 1000ms.  Clearly,
       the walls of such a hall aren’t far away, so you should define its set-
       ting  be	 given	every wall its delay time.  However, if the wall is to
       far away for the reverb time, you won’t hear the reverb, so the nearest
       wall will be best at "t/4" delay and the farthest at "t/2". You can try
       other distances as well, but it won’t sound very realistic.  The	 walls
       shouldn’t  stand	 to  close to each other and not in a multiple integer
       distance to each other ( so avoid wall like: 200.0 and 202.0, or	 some-
       thing like 100.0 and 200.0 ).

       Since  audience	halls  do have a lot of walls, we will start designing
       one beginning with one wall:

	     play file.xxx reverb 1.0 600.0 180.0

       One wall more:

	     play file.xxx reverb 1.0 600.0 180.0 200.0

       Next two walls:

	     play file.xxx reverb 1.0 600.0 180.0 200.0 220.0 240.0

       Now, why not a futuristic hall with six walls:

	     play file.xxx reverb 1.0 600.0  180.0  200.0  220.0  240.0	 280.0
       300.0

       If  you	run out of machine power or memory, then stop as many applica-
       tions as possible (every interrupt will consume a lot of CPU time which
       for bigger halls is absolutely necessary).

       Phaser

       The  phaser  effect  is	like  the flanger effect, but it uses a reverb
       instead of an echo and does phase shifting. You’ll hear the  difference
       in the examples comparing both effects (simply change the effect name).
       The delay modulation can be sinusoidal or triangular, preferable is the
       later for multiple instruments. For single instrument sounds, the sinu-
       soidal phaser effect will give a sharper	 phasing  effect.   The	 decay
       shouldn’t  be  to  close	 to 1.0 which will cause dramatic feedback.  A
       good range is about 0.5 to 0.1 for the decay.

       We will take a parameter setting as for the flanger before (gain-out is
       lower since feedback can raise the output dramatically):

	     play file.xxx phaser 0.8 0.74 3.0 0.4 0.5 -t

       The drunken loudspeaker system (now less alcohol):

	     play file.xxx phaser 0.9 0.85 4.0 0.23 1.3 -s

       A popular sound of the sample is as follows:

	     play file.xxx phaser 0.89 0.85 1.0 0.24 2.0 -t

       The sample sounds if ten springs are in your ears:

	     play file.xxx phaser 0.6 0.66 3.0 0.6 2.0 -t

       Compander

       The  compander  effect  allows the dynamic range of a signal to be com-
       pressed or expanded.  For most situations, the attack time (response to
       the music getting louder) should be shorter than the decay time because
       our ears are more sensitive to suddenly loud  music  than  to  suddenly
       soft music.

       For  example,  suppose  you  are	 listening  to	Strauss’  "Also Sprach
       Zarathustra" in a noisy environment such as a car.  If you turn up  the
       volume  enough  to hear the soft passages over the road noise, the loud
       sections will be too loud.  You could try this:

	     play file.xxx compand 0.3,1 -90,-90,-70,-70,-60,-20,0,0 -5 0 0.2

       The transfer function ("-90,...") says that very	 soft  sounds  between
       -90  and	 -70 decibels (-90 is about the limit of 16-bit encoding) will
       remain unchanged.  That keeps the compander from boosting the volume on
       "silent"	 passages  such	 as between movements.	However, sounds in the
       range -60 decibels to 0 decibels (maximum volume) will  be  boosted  so
       that  the  60-dB dynamic range of the original music will be compressed
       3-to-1 into a 20-dB range, which is wide enough to enjoy the music  but
       narrow  enough  to get around the road noise.  The -5 dB output gain is
       needed to avoid clipping (the number is inexact,	 and  was  derived  by
       experimentation).   The	0  for the initial volume will work fine for a
       clip that starts with a bit of silence, and the delay of	 0.2  has  the
       effect  of  causing the compander to react a bit more quickly to sudden
       volume changes.

       Changing the Rate of Playback

       You can use stretch to change the rate of playback of an	 audio	sample
       while preserving the pitch.  For example to play at 1/2 the speed:

	     play file.wav stretch 2

       To play a file at twice the speed:

	     play file.wav stretch .5

       Other  related  options	are  "speed"  to change the speed of play (and
       changing the pitch accordingly), and pitch, to alter  the  pitch	 of  a
       sample.	For example to speed a sample so it plays in 1/2 the time (for
       those Mickey Mouse voices):

	     play file.wav speed 2

       To raise the pitch of a sample 1 while note (100 cents):

	     play file.wav pitch 100



       Reducing noise in a recording

       First find a period of silence in your recording, such as the beginning
       or  end	of  a  piece.  If  the	first 1.5 seconds of the recording are
       silent, do


	       sox file.wav -t nul /dev/null trim 0 1.5 noiseprof /tmp/profile

       Next, use the noisered effect to actually reduce the noise:


	       play file.wav noisered /tmp/profile



       Other effects (copy, rate, avg, stat, vibro, lowp, highp, band, reverb)

       The other effects are simple to use. However, an "easy to  use  manual"
       should be given here.

       More effects (to do !)

       There  are  a lot of effects around like noise gates, compressors, waw-
       waw, stereo effects and so on. They should be implemented,  making  SoX
       more  useful  in	 sound	mixing techniques coming together with a great
       variety of different sound effects.

       Combining effects by using them in parallel or  serially	 on  different
       channels	 needs	some  easy  mechanism which is stable for use in real-
       time.

       Really missing are the  the  changing  of  the  parameters  and	start-
       ing/stopping of effects while playing samples in real-time!

       Good luck and have fun with all the effects!

	    Juergen Mueller	     ([e-mail])


SEE ALSO
       sox(1), play(1), rec(1)

AUTHOR
       Juergen Mueller	   ([e-mail])

       Updates by Anonymous.



			       December 11, 2001			SoX(1)