isolating bass

[gord29]

I was trying to isolate the bass part of this song so I could learn it easier. I used the low pass filter and that made quite a difference but there was still a lot of the other guitar, organ etc. Is there a way to further eliminate the higher frequency things?

[Robert J. H.]

What song? Is it in stereo?

[steve]

Set the "Rolloff (dB per octave)" to "48 dB".
For a more pronounced cut-off you can apply the effect more than once.

More information: http://manual.audacityteam.org/o/man/lo ... ilter.html

[DVDdoug]

There are 2 problems -

1. A bass is only one octave below a guitar, and since you are not always playing in the lowest octave there is a lot of overlap. An organ can go at least as low as a bass. If there's a kick drum that's one more sound you can't filter-out while leaving the bass.

2. You need to hear the bass harmonics which will extend well into the guitar range. I've noticed that many bass cabinets have a tweeter horn... That's for the harmonics.

If you have a good subwoofer, that should help. A cheap-boomy one-note subwoofer might be worse than no sub. Or, you might try playing the file through your bass amp & cabinet.

You might also have better luck just boosting the bass and leaving everything else. (After boosting anything, it's a good idea to run Amplify to bring the peaks down to 0dB to avoid clipping/distortion.)

Or... If you know more about music than me... Maybe you can figure-out the melody & cord progression and then figure-out what the bass notes should be????

[gord29]

The song is the Barney Miller theme. The opening four measures are easy to nail perfectly-you can hear whats going on but add to that you can use Audacity to change the tempo and it slows way down without changing the pitch. In the rest of the song they are using likely the F major pentatonic scale to noodle around on. You can hear that too but I was just trying to tweak it as much as possible to isolate the bass (and learn more about using Audacity). Even here you can take a section at a time and slow that down and get it perfect...but to copy something note for note is not making music so I'm not trying to copy but capture the spirit or mood and do my own version. In fact thats what they did over the seasons Barny Miller played. There were several versions or takeoffs from that original. I'll try that roll off too. Thanks all!

[gord29]

What song? Is it in stereo?

http://www.youtube.com/watch?v=A_TJGYglTaM Barney Miller Theme. This is the best version I've found on youtube.

[Robert J. H.]

What song? Is it in stereo?

http://www.youtube.com/watch?v=A_TJGYglTaM Barney Miller Theme. This is the best version I've found on youtube.

Thank you.
The easiest way and the least expensive low pass filtering can be achieved by simply down-sampling the audio. The remaining frequency are below half of the sample rate.

bass-line.mp3

(144.91 KiB) Downloaded 717 times

I've re-sampled to 1500 Hz and removed also frequencies above 400 Hz.
the bass line isn't that hard to figure out now. There's a modulation towards another key in the last bars.

[gord29]

The easiest way and the least expensive low pass filtering can be achieved by simply down-sampling the audio. The remaining frequency are below half of the sample rate.
bass-line.mp3(144.91 KiB) Not downloaded yet
I've re-sampled to 1500 Hz and removed also frequencies above 400 Hz.
the bass line isn't that hard to figure out now. There's a modulation towards another key in the last bars.Robert J. H. Posts: 656Joined: Thu May 31, 2012 8:33 am

Thanks! that really helps. I don't really understand the terminology that well. Could you explain some plz? I know what low pass filtering means and how to use it in Audacity but down-sampling-that must mean something more than just recording a few measures of music? How do you set the sample rate? and remaining frequency are below half of the sample rate. I don't see what's going on there or how it works.

[Robert J. H.]

Sorry, if I flooded you with those technical terms.
As you might know, music is converted from analog to digital domain by measuring voltage in certain intervals. For a CD, this is 44100 times per second (i.e. Hz) or 44.1 kHz.
Conversly, the sample values are turned into alternating current to excite the membrane of a speaker.
The highest frequency we can reach (by compressing and expanding the air before the speaker membrane) is by the digital serie (sample values) '1 -1 1 -1 1 -1 ...'. This means that we can max produce 22050 '1 -1' pairs with a sample rate of 44.1 kHz.
Down sampling means that we choose a smaller amount of samples per second. Above, I've taken 1500 Hz which can only produce sounds up to 750 Hz. In order to prevent the sound from having nasty ringing artefacts (so called aliasing), a low pass filter is used by the re-sampling algorithm.
There's essentially no difference between using a low-pass filter and re-sampling the audio except that you can save 20 to 40 times more bass lines with the latter method. The attached mp3 holds all needed information in a 144 kB lengthy file. It has a sample rate of 8000 Hz but only a part of the whole spectrum is actually used.
The Resample option can be found in the track menu. Remember to enter double the value of the lower frequency band you want to preserve, e.g. 1800 for frequencies up to 900 Hz.
I've asked you further if the audio was stereo. because the bass is almost always placed in the middle of the stereo field and by extracting the center panned portion, you can easily get rid of a lot of other instruments.
In this case, the you tube video is mono, but the line isn't that hard to transcribe with simple low-passing.

[gord29]

Thanks again I think I understand most of that. It's good to learn stuff. Now I can do it on my own. Originally I didn't think I needed or wanted to get it down note for note but now I'll do that because I can hear it more clearly and it will help me learn bass better. And it's interesting how when you slow a piece down you hear definite phrases like a complete sentence or thought (which you can then learn) unlike before when I only heard a longer solo.