To isolate the left-hand of a piano song


I found a nice piano song on youtube that I tried to transcript. I had no problem with the right-hand because the video camera was placed on the right of the player but the left-hand got me more into trouble because it is more than easy chords. There is a kind of melody hidden behind the right-handed one and when I play what I’ve transcripted, I’m like “No, it’s not so good”.

So I remembered me Audacity.

My first idea was to use a low-pass filter (cutting frequence: 250 Hz (between Sib2 en Do3)) to isolate the low register. I used a -36dB decrease. I was really astonished to hear almost nothing after that. I know that -36dB is strong but it also decreases the most the high register.

So I amplified that within the saturation. That was beter but still very very low and difficult to hear so I changed the tone by 3 octaves. It’s beter but it still remains the harmonics of the low register. But it helps me a bit. I wonder if you have a beter solution with all the experience you have.

So, I summarrize my idea:

  • low-pass filter (cutting frequency: 250 Hz)
  • Amplification
  • Tonality modulation

Thanks for your suggestions!


I know that -36dB is strong but it also decreases the most the high register.

That is its job. You probably will not be able to isolate the left hand like that. Piano notes are complex and rich with overtones and harmonics. When you get to the lowest octave, the sound is mostly the hammer hitting the string which is all overtones and almost no musical note.

That’s why when you peeled off all the overtones (-36dB), almost everything vanished. If you remove enough overtone sound, the attack and release of the note will get mushy too. Each note will fade in and out making it almost impossible to tell what the fingering was.

If you allow a lot of overtones to pass, the other fingerings will be heard.


There’s another possibility, too. Most people’s music system won’t respond to the lowest piano notes—the real notes, like the lowest organ pedals. So if you peel away the overtones and harmonics in Audacity you’re left with…nothing. I think that’s what actually happened. I have several headphone and speaker systems that won’t play organ pedals or low piano notes. It’s not that unusual.


You have a picture of that don’t you koz? I can’t locate it now, but I think the spectrum plot of a piano note explains the problem. Do you have that picture handy?

I sorta remember that’s an analysis of the first note of this “performance.”