Recording your wavfiles

• CLEAN YOUR RECORDS AS WELL AS POSSIBLE!!  The safest method is to use distilled water, and spray it on with a perfectly clean spray bottle.  Let it sit for a few minutes and then wipe it off with clean, soft, pure cotton cloth. Don't do this on the turntable itself, lay the record on a soft cloth on top of a firm flat surface.  Any lint from the that gets on the record from the cloth will come off easily with your regular record duster that you will apply while the record is on the turntable and spinning.  There are plenty of places on the internet that have suggestions for how to clean LP's.  The other thing to try is to play the LP once before you copy it to disk, the action of the needle in the groove may be able to dislodge more remaining particles.

• Make sure cpu and memory intensive apps are not running !!
  For example the setiathome client uses enough of both to really make the playback (and recording) not be able to get data to and from the hard drive to the audio device.

• Record your track(s). I now use a tool like brec for OSS and arec for ALSA, and record a number of tracks (i.e. one entire side of an LP at once). Because GWC can handle extremely large audio files, it is more convenient to work with one single file. Using cdrdao to burn the CD's also allows the use of a single audio file. Be sure to get some "silent" audio at the start of each track, this information is used by gwc to assess the background noise level for noise elimination.

An important note on GWC editing

Selecting regions

• This is how you identify regions of audio for GWC to perform tasks upon, it is done by highlighting a portion of the displayed audio waveform with the standard click and drag method using the mouse.
• If you position your cursor between the left and right channels while you highlight, you will select both channels, but if you move the cursor up or down when you make the selection, you can select either the left channel, or the right channel indepedently.
• There are 200 markers available. You set them by using the "B" and "E" keys, and clear them using the "Markers:Clear Markers" menu item. "B" toggles the first marker at the start of the currently selected region. "E" toggles the second marker at the end of the currently selected region.
• While you are selecting a region, if the cursor gets within 10 pixels of a marker, it will "snap" to that marker. This allows you to zoom in to a portion of the audio data, set a marker, zoom and pan to another portion, set another marker, and then zoom back out and select the region between the markers -- giving you a fine level of control on the precision of the selected region.
• You may also press the 'm' key, to automatically select the region between markers. A button and icon are in the works...

Steps to restore audio quality

• Denoise

• Select the sample region, make sure the sample region is entirely free of music.
• If you have a "clean" LP, i.e. almost no crackle in the "silent" region (you may the declicker in the silent region to remove a few clicks, but make sure the result doesn't sound goofy)
• Press the sample noise button (the one with the eyedropper)
• Now select and test denoising on a couple of different areas on the audio file, just to be sure it works.  Take the defaults of:
FFT Size=4096
reduction=0.5
smoothness=11
number of samples=16
gamma=0.95
Windowing Function=Hanning-overlap-add
Noise Suppresion Method=Lorber & Hoeldrich
• Try denoising a few seconds at the start of the track (include some of the pre-track noise section to see how good the denoise algorithm works on pure noise). Play the denoised region, see if you like it. Now do an Edit->undo (Ctrl-Z)
  
  Repeat the above process at the end of the track and some place in the middle. This gives you a good idea of how the noise sample a the start of the track will work as an estimate of the actual noise at the middle and end of the track.
  
  If you find the result sounds "metallic" or "burbly", back off on the reduction amount, remember to use Edit->undo (Ctrl-Z). You can also try varying the gamma factor. I have found if it gets too close to 1.0, it can distort the final sound a little. Anything between 0.5 and 0.99 is probably worth trying.

• When you are satisfied you have the settings you want, go for the gold and select the entire track and denoise the whole thing. In most cases the defaults given above will work quite well, so don't think this is hard, it's really easy! At this point you may skip saving the undo data, which for most songs is 10's of megabytes and will take some time to save.

• Declicking

• The highest quality declicking really needs to be done "manually".  I have had cases where it has a "false positive", and inadvertently degrades the signal in a few places.  I do manual declicking by either going to sonogram view, and looking for spikes, or just listening and highlighting an area around where I hear the click. There is no better click detector than your ears! I have found for a window which is 600 pixels wide, about 22050 samples (about 1/2 second at the 44100 Hz sample rate, which is CD quality...) displayed in the sonogram view works quite well.
• There is an FFT click detector implemented now. The settings are the dB above average that the click amplitude must be in order to be marked and or fixed. Humans generally can detect a 3 dB change, so that's the default level for weak click detection. While the FFT click detector appears to work better, it is only based on some limited observations of mine, and it is MUCH SLOWER.
• If you are working on a track that you are less concerned about the final quality, then you can select a large region and use the declick strong clicks button. This works reasonably well.
• <HINT> - use the spacebar to start and stop playback!!!
  left hand on spacebar, right hand on mouse - very efficient.
  You can get a good idea where the click is by watching where the cursor is when you hear the click</HINT>

• If you hit the "s" key during playback, gwc will stop the playback and highlight the last 1/2 second of audio played

• There are 3 levels of declicking
1. Declick-strong - searches for and repairs the loudest clicks
2. Declick-weak - searches for and repairs weaker clicks
3. Declick-manual - If neither of the above methods worked to find the click, you can zoom in on the click by listening, highlighting, zooming in on the selection as described above. Then, making sure you have only the damaged portion of the audio data selected (in most cases this will be less than 100 samples), push this button, and it repairs the highlighted selection (or current view) -- don't use on more than about 200 samples!
• In general you should start with Declick-strong , and use Declick-manual as your last resort.

• De-crackling

  -- that sound of bacon frying on your audio track. Crackle is mostly a bunch of closely spaced clicks. First try the decrackling algorithm. Use the default settings in preferences. If that fails you, I have had success at times by repeatedly applying the "remove strong clicks" filter over an area until the reported repairs is zero.

• Estimating

  Sometimes, there are large sections in the audio (200 to 8000 samples), that are just bad. It may sound like a "thunk" or a dropout. The estimation repair looks at the frequencies to the left and right of the selection (or current view), and blends those frequencies across the repair area. The result will be better than what was there to begin with, as of version 0.20-08 this works quite well, but remember, UNDO is your friend!

• Finishing up

  • Eliminate blank portions at start and end of track -- highlight the area at the start of the track and use the scissors icon to indicate you want that deleted, do the same for the end of the track.  You can't eliminate sections in the middle of the track.  Umm, I haven't tested what would happen if you tried, it could be bad. Always back up your data :-)

  • You may want to look at the reverb and DSP filters if the audio needs a little bit of "presence". They are documented in the main help file for GWC
  • Exit. -- gwc will ask if you really want to save your changes

• I wrote a little utility -- wavlist, which will list the *.wav files and append the time in minutes:sec to the list so you can use it with something like gcover to create jewel case covers.

KEYBOARD FUNCTIONS:

• spacebar - starts and stops playback
• 'a' - Creates or appends "cdrdao.toc", with the currently selected or viewd audio segment.
• 'Alt-a' - Apply sample restoration algorithm (declick),to the currently selected (or viewed) audio segment
• 'u' - increase the scale on audio display
• 'd' - decrease the scale on audio display
• 'm' - select the region between the markers
• 'r' - reset the scale on audio display to 1.0
• 's' - stop playback, and automatically highlight last 1/2 second of audio played
• 'z' - zoom in on the selected region
• B - this will toggle the marker at the start of the currently selected region
• E - this will toggle the marker at the end of the currently selected region