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BOOT CAMP 453 (05/12/06)
Vinyl and Tape to CD and MP3, part 4
We have reached the penultimate episode in this
short tutorial on using your PC to preserve your treasured vinyl records and
cassette tapes. At this point in the proceedings you should have your first
recording of a track or one side of an album on your PC. This week’s task is to
clean it up in readiness for the final stage of creating an audio CD or MP3
file.
Start by creating a new ‘master’ music folder
on your hard drive and within it, sub folders for each album you’ll be working
on. Use ‘Save Project’ on Audacity’s File menu to name your recording and put
it into its relevant subfolder where it will be saved in Audacity’s native
‘project’ file format (extension *.aup). If you recorded the side of an album
as one track then now would be a good time to split it into separate tracks
using the method outlined last week.
The first job is to remove any loud ‘pops’ or
‘clicks’ as they are extremely annoying and make it harder to get rid of
low-level noise. Audacity has a Click Removal tool -- on the Effects menu --
and it works well but I suggest you try this manual method first. It is more
discriminating and a very good way of getting used to Audacity’s editing
tools.
Pops and clicks are normally easy to spot and
show up as short sharp spikes on the waveform. Find your first click, either by
listening to the track and noting the time index, or looking for the
characteristic spike on the waveform. Use the scroll bar at the bottom of the
screen to centre the click on the track display then select the magnifying
glass tool and place it over the spike. Tap the left mouse button and you will
gradually ‘zoom’ in on it. Keep clicking until you can see the individual
‘samples’, represented by tiny dots on the waveform.
When you can see all of the dots that make up
the spike click on the pencil-shaped ‘Draw Tool’. The dots will be highlighted
and you can use the Tool to ‘drag’ the peaks down to smooth out the waveform.
Use the Magnifying Glass tool to zoom back out again, click the ‘I’ bar
Selection tool a few seconds ahead of where the pop used to be and click Play
to hear how it now sounds. Hopefully you won’t know it was there. Repeat as
necessary but don’t become obsessive, only tackle the very worst ones at this
stage. Save the modified track but this time give it a new name (e.g. save
Track 1 as Track 1a). This gives you the option to go back and start over with
your original recording if you are unhappy with the end result.
Next we’re going to tackle hiss and crackle.
The Noise Removal tool on Audacity’s Effects menu is very effective at
eliminating the sort of low-level surface noise you hear on well-used LPs and
worn tapes. It’s more than just a simple filter, though and it uses a sample of
the noise on the recording to discriminate between wanted and unwanted sounds.
The first step is highlight few seconds of a silent part of the recording --
usually at the beginning or the end of a track. Now go to Effects > Noise
Removal and click the Get Noise Profile button. Highlight the whole track (or
the section) you want to de-hiss then use the Less/More slider and Preview
buttons to filter the noise and judge the effect. When you are satisfied that
it’s as good as it is going to get click the Remove Noise button and re-save
the file.
We’ll round off with a couple of tweaks that
can help to improve the sound of your recording. Audacity has a sophisticated
‘Equalizer’ that lets you create a custom ‘Response’ curve to boost or
attenuate frequencies or groups of frequencies. It also has a set of
‘predefined‘ curves, to tailor the sound to compensate for the characteristics
of particular makes and types of turntable. It’s very easy to use. Highlight
all or part of a recording and click Equalization on the Effects menu. To
create a curve manually click on the broad blue line at a point that
corresponds to the frequency band you want to adjust, and move the line up or
down.
You might also like to try Audacity’s FFT (Fast
Fourier Transform) tool, which works in a similar manner to the Equalizer but
provides more precise adjustment over narrower bands of frequencies.
We’ve only scratched the surface of what
Audacity can do (see this week’s Top Tip) but using just the basic click and
noise removal tools it is possible to transform an old recording. Don’t be put
off if your first efforts are not up to professional standards, take your time
and refine your technique. Don’t forget Audacity has an unlimited undo facility
(between saves), and if it all goes horribly wrong you can always start again
from scratch using your original recordings.
Next Week -- Vinyl and Tape to CD and MP3, pt 5
JARGON FILTER
EQUALISER
A
sophisticated tone control that provides precise adjustment over bass,
mid-range and treble frequencies
FFT
Fast Fourier Transform; algorithm used to solve the complex
mathematical equations used in digital signal processing systems
SAMPLE
A ‘snapshot’ of a signal, taken many thousands (or millions) of
times a second and converted into a numeric or digital value
TOP TIP
Here are some more Audacity Effects that you might find useful
when processing old recordings. Change Speed works like the speed control on a
record player or turntable so if your original recording is playing back at the
wrong speed this Effect can compensate. Change Tempo does a similar job but
without changing the pitch of the recorded sound. The Compressor changes the
recording’s dynamic range by altering the balance between the louder and
quieter parts of a recording. This can help to improve sound quality in noisy
environments, such as listening to music in a car or on a personal stereo.
---end---
© R. Maybury 2006, 2911
Part 1 2 3 5
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