hpr-knowledge-base/hpr_transcripts/hpr1796.txt

Episode: 1796
Title: HPR1796: Audacity - Chains, Notches and Labels
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1796/hpr1796.mp3
Transcribed: 2025-10-18 09:24:02

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Hi, I hack in public radio listeners, my name is Krause, this is my first time recording.
I often go by the username Cheeto4493 on emails and stuff like that.
I'm not much of a social person, so you probably won't find me on Twitter or anything,
any of the other social things like Facebook.
I vote Ken Fallon a show for quite a while, but I didn't know what to exactly to talk
about.
I've been wanting to do something on the Raspberry Pi, but haven't come up with a good project yet.
All the projects I've been wanting to do just haven't come to fruition.
Then another project on my back burner that I'm fixing to start that's a how to automate my
window blind. So hopefully you may be hearing that come up on the list in a few months.
What I wanted to talk to you today about was Audacity and some tips and tricks
after listening to John podcast on label track. I just wanted to add a little bit to that and a
a few couple other tricks that I use often. John talked about labeling tracks for
kind of help sorting things out. What I use it for a lot of times is exporting
the actual sound as individual files. A lot of times what I'll do is record like a whole
album off of a record or tape and then want to transfer it digitally. If you label each one
of those sections and then you can go into export multiple and you'll actually take the labels
and use those as your file names. One of the things that I found really helpful is if you look
over there under file and import you can actually import label tracks. What it is is uses a tab separated
text file. On each line is the starting position tab ending position tab and then the label name.
And so what you can do is if you have a album let's say that you know how long each song is
you can go through and put all those into a text file with say the first song is 360 seconds long
and you can start at zero and then tab and then 360 and then tab and then your label of your first
track and then start a new line and then your next track if it starts at 360 or
360 seconds you put that in your first line and then tab over and then put in the
the additional say your next track is 100 seconds long then it would be 462 and you just
basically keep running total of your time all the way through and you just save that as a text
file and then you can import that into audacity in your project and it will create a label track
underneath and show all of those labels. I think this might be real helpful if you are doing a
recording at say like a conference and you just start the recorder at the beginning of a top
and if you've got a notepad there handy you can just in a stopwatch you can just write down the
times of different like speakers starting and stopping and the names and then you can import
all that in as one long track if you're not sitting there hitting the stop and record each time
and then it will divide those up and label them for you by using the import feature.
Once you import your labels if you look at that label track you'll notice that in between each label
is like a greater than less than sign in a circle in the middle just kind of a small icon can actually
bump them each one over to the appropriate start of that track. If you find you have like a long
seconds between sections you can actually click on like the greater than symbol and actually
slide it to the right and it will move the following track down and leave a gap in between that
when you do an export it won't export that silence so that's another oh handy trick there of
how to adjust your times. One of the other tricks I wanted to talk to you about today was
notch filters and a notch filter is basically a way of removing it's kind of like an equalizer
at a specific frequency and I don't think this comes standard in audacity I've actually imported
the add-ons and I think it is down in the bottom section of additional plugins for
audacity and it's called notch filter. Here in America our main frequency is at 60 hertz and a
lot of times your equipment sometimes they'll pick up sounds based around that frequency and the
best way to find out this will work for you is to highlight a section of silence that has the
noise in the background on your track just by clicking and dragging a little section of it a
couple of seconds long and then if you go up into analyze and click on plot spectrum
it'll pop up a little window and on that you'll see a graph and if your graph shows some spikes
at some frequencies this is a good time to use a notch filter because a notch filter will take out
the spikes when I do this I find three spikes on my recordings I think I have an issue between my
mixer and my recorder where I usually do recordings that picks up a 60 hertz a 120 hertz
and a 180 hertz hum and for some reason the 180 hertz is worse than the 60 hertz I think it's
kind of an additional by adding the frequencies together you get a stronger attenuation there at each
frequency so what you can do is once you find the frequencies that you need to filter if you'll go
into back to your track and highlight the sections you want to take the noise out of usually I just do
the whole track and then go up and click notch filter you'll find it'll pop up and you can insert
the frequency so I usually start with 60 and then underneath that is Q and that is your how wide
of a frequency band you're going to cut down and I default is one and I usually go to 10 I find that
a good number to start at usually takes out just enough but doesn't overlap into the other frequencies
and you hit ok and apply that then I go up to it and hit notch filter again and do it with the
120 hertz and then I do the third time at the 180 hertz and I'll add it in some audio clips here
and so you can hear the differences in that versus using the noise removal tool that's built
into audacity this is a test recording unmodified this is with notch filters and this is with
noise removal used sometimes especially on an audio recording that's not very loud for the speakers
not too very close to the mic and so you have a lot of background noise especially if you have
like I said spikes on your plot spectrum that are noise frequencies that if you try doing just
noise removal tool it will make your audio not sound as good it actually takes out too much
frequencies in the area where you're talking as opposed to the notch filter which takes out
frequencies of specific notches and the third thing I want to talk about today was chains often when
I'm editing files and audacity I find that I'm repeating the same tasks every time I do a file
like normalize to bring up the volume levels a lot of times I'll do a run the leveler
which kind of levels out the highs and the lows so if you get somebody who's real dynamic and
they're speaking it's real loud and then they get quiet and then a little loud again
leveler really helps bring that down to a consistent volume level then I apply the notch filter
like three times and then after I'm done with the filter I usually end the leveler I go through
and I normalize it one more time and then the last thing I do is export it as a different like MP3 file
well if you do the same thing over and over again chains is real handy for that
because it basically what you're doing is chaining those tools together if you go over to file and
down to modify chains you'll see you'll pop it up you'll see there's already one built into
audacity called I think it's called MP3 conversion I believe it is if you look on the right it'll say
MP3 export and basically what you see on that right tab is what you're doing each time
and see you can go down there to the bottom and you can click add and then it'll pop up a little
window and you choose what you want to modify if you choose normalize and then you can go in and
adjust your basically what I would say your default settings for that modifier save it
and then you can insert another and so like I said I usually do I add them in in the order
that I normally do normalize leveler and then my three notch filters and then the last thing
you can do is to export and then end is then the very last thing there save that save it as a
name you'll recognize I use to call it something like clean audio file over there and so what you do
is you can once you've got your chain setup click on file and use chains and then pull up the chain
you want to use and apply it to your track and it'll do all those steps all at once it saves it
but the one of the neat features of the chains is you can apply it to multiple files
without even opening the file up to edit it if you go up to chains and apply chains and multiple
files you just click the files that you want to do they all have to be in the same directory
and then apply chains and it'll open the file apply the chain and then if you have export
MP3 or export org setting your thing it'll export those into a sub directory called clean
in your same directory it opened them in and that's a good way to do bulk files so if you've got
several files that you want to change it once it's a good way to do that I have to learn
scripting to do it in a command line to open up and apply all those things but I hope you've
learned something from my tips and tricks today and hopefully it won't be too long before I
do another podcast recording thank you and have a good day
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