使用BS4解析HTML表(Parsing HTML Tables with BS4)

 在Audacity中，您必须选中首选项的“ 导入/导出”部分中的 “使用自定义混合”单选按钮。 这将允许您导出多声道文件，并手动将曲目分配给频道。 
 
 除此之外，普通的旧.wav可以正常工作。 
 
 但您也可以使用SoX以更自动化的方式创建文件。 
 
 手动，您可以将五个不同的文件组合（或“合并”，如文档中所述）五个不同的文件，如下所示： 
 
sox -M chan1.wav chan2.wav chan3.wav chan4.wav chan5.wav multi.wav
 
 为了自动化这个过程，我整理了一个简短的Bash例程，用于生成具有交错测试音的多声道文件： 
 
NUM=5    # Number of channels
LEN=2    # Length of each test tone, in seconds
OVL=0.5  # Overlap between test tones, in seconds

# A one-channel base file containing simple white noise.
# faded at both end with a quarter wave envelope to ensure 
# smooth equal power transitions
sox -n -b 24 -c 1 out.wav synth $LEN whitenoise fade q $OVL -0 $OVL

# Instead of white noise you can for example make a 1kHz tone
# like this:
# sox -n -b 24 -c 1 out.wav synth $LEN sine 1k fade q $OVL -0 $OVL

# Or a sweep from 10Hz to 10kHz like this:
# sox -n -b 24 -c 1 out.wav synth $LEN sine 10-10k fade q $OVL -0 $OVL

# Produces a sequence of the number of seconds each channel
# shall be padded with
SEQ=$(for ((i=1; i<=NUM; i++))
do 
  echo "$i 1 - [$LEN $OVL -]x * p" | dc  # reverse-Polish arithmetic
done)

echo $SEQ

# Padding the base file to various degrees and saving them separately
for j in $SEQ
do 
  sox -c 1 out.wav outpad${j}.wav pad $j
done

# Finding the just-produced individual files
FIL=$(ls | grep ^outpad)

# Merging the individual files into a single multi-channel file
sox -M $FIL multi.wav

rm $FIL  # removing the individual files

# Producing a multi-channel waveform plot
ffmpeg -i multi.wav -y -filter_complex "showwavespic=s=2400x900:split_channels=1" -frames:v 1 waveform.png

# displaying the waveform plot
open waveform.png
 
 如波形图清晰显示，结果由一个包含五个通道的文件组成，每个通道具有相同的内容，只是在一段时间内移动： 
 
  
 
 更多关于使用dc反向波兰算法： http ： //wiki.bash-hackers.org/howto/calculate-dc 
 
 有关使用ffmpeg显示波形的更多信息： https ： //trac.ffmpeg.org/wiki/Waveform 

In Audacity you have to check the 'Use custom mix' radio button in the Import/Export section of the preferences. This will let you export multi-channel files, and manually assign tracks to channels.
 
Other than that, plain old .wav works fine for this.
 
But you can also use SoX to create the files in a more automated manner.
 
Manually you can combine (or 'merge' as it's referred to in the documentation) five distinct files into a single five-channel file like this:
 
sox -M chan1.wav chan2.wav chan3.wav chan4.wav chan5.wav multi.wav
 
To automate the process I put together a short Bash routine for producing a multichannel file with staggered test tones:
 
NUM=5    # Number of channels
LEN=2    # Length of each test tone, in seconds
OVL=0.5  # Overlap between test tones, in seconds

# A one-channel base file containing simple white noise.
# faded at both end with a quarter wave envelope to ensure 
# smooth equal power transitions
sox -n -b 24 -c 1 out.wav synth $LEN whitenoise fade q $OVL -0 $OVL

# Instead of white noise you can for example make a 1kHz tone
# like this:
# sox -n -b 24 -c 1 out.wav synth $LEN sine 1k fade q $OVL -0 $OVL

# Or a sweep from 10Hz to 10kHz like this:
# sox -n -b 24 -c 1 out.wav synth $LEN sine 10-10k fade q $OVL -0 $OVL

# Produces a sequence of the number of seconds each channel
# shall be padded with
SEQ=$(for ((i=1; i<=NUM; i++))
do 
  echo "$i 1 - [$LEN $OVL -]x * p" | dc  # reverse-Polish arithmetic
done)

echo $SEQ

# Padding the base file to various degrees and saving them separately
for j in $SEQ
do 
  sox -c 1 out.wav outpad${j}.wav pad $j
done

# Finding the just-produced individual files
FIL=$(ls | grep ^outpad)

# Merging the individual files into a single multi-channel file
sox -M $FIL multi.wav

rm $FIL  # removing the individual files

# Producing a multi-channel waveform plot
ffmpeg -i multi.wav -y -filter_complex "showwavespic=s=2400x900:split_channels=1" -frames:v 1 waveform.png

# displaying the waveform plot
open waveform.png
 
As the waveform plot clearly shows, the result consists of a file with five channels, each with the same content, just moved about some in time:
 
 
More on reverse-Polish arithmetic using dc: http://wiki.bash-hackers.org/howto/calculate-dc
 
More on displaying waveforms using ffmpeg: https://trac.ffmpeg.org/wiki/Waveform