Improving and Remastering Audio: Advanced Steps and Tips

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This article was written for a now obsolete 1.3 Beta version of Audacity so until it is updated, some material may not be accurate for current Audacity.

Peter 3May14: Gale has commented on its sister page Improving and Remastering Audio.

• Peter 9Jun14: Following a suggestion from Steve on the Forum, this page and it's sister article are slated to remain on the Wiki but be updated to become version-neutral with links to the manual for how-tos.

 

This is part 2 of an article intended to provide a first but detailed guideline to those who want to clean up poor quality audio files, for example those who are starting to digitize their record or tape collection and want to do a little more than just transfer them to their hard disk with their existing quality. The bulk of the article deals with editing one single audio file. In part D is a section about preparing a set of files for a CD or a playlist.

Related article(s): Improving and Remastering Audio Transferring tapes and records to computer or CD Noise Removal Click Removal Tutorial in German about using Audacity effects with real-time control.  "Einführung in alle gängigen Effekte der Musikproduktion"  More detailed tutorial in German about all effects.

Main Article	Advanced Steps and Tips
Preliminary Notes Editing - General Editing - The Individual Steps Two-Channel Mono Files Unwanted Parts Removal (Trim) DC Offset Removal Noise Reduction Clicks, Pops, Dropouts Removal Pan Correction Frequency Spectrum Editing (Equalization) Volume Editing (Amplify / Envelope) Dynamics Editing Reconstructing Missing Parts	Advanced Steps Batch Processing For Files (Apply Chain) CD Or Playlist, Preparations Re-Vinylize Tips

Advanced Steps

Batch Processing For Files (Apply Chain)

In a situatiion, where identical tasks have to been carried out on several files, batch processing comes handy. In a script you define what tasks to do and how, then you decide on wich files the process shall work.

The sripts containing the tasks to be done und their parameters are called "chains", running a batch process is called "applying a chain".

Some chains are pre-installed, others may be defined (and saved) by you.

Audacity distinguishes between two modes:

• acting on all files of a project or
• acting on a set of files.

These notes concern the mode "acting on a set of files".

• How to add own chains

1. Select File > Edit Chains....
   The new window shows the existing chains on the left, the commands and parameters of the selected chain on the right.
2. To define a new chain, click "Add" below the left list, enter a name, click "OK" (New chains are saved automatically under the entered name and are listed the next time). A new "torso" chain appears on the right with a first entry "-END-".
3. Insert commands by clicking "Insert" below the commands list. The "Select Command" window appears.
4. Select a command by doubleclicking it, its name has to show at the top!
5. If there are parameters and you want to change them, click "Edit Parameters", edit them. Some commands use current parameters, e.g. "ExportMp3" uses the currently set bitrate.
6. Click "OK".
7. Repeat from step 3 ("Insert"), until done.
8. Arrange the commands using the buttons below the commands list.
9. Click "OK" bottom right.

The last command before "-END-" has to be an "Export".
Else the chain processing is carried out without any results.
The initial import is done without the need of a command.

"Amplify" may cause clipping.

"TruncateSilence" also effects silence within your files.

• How to a apply a chain

1. With no file loaded into Audacity select File > Apply Chain...
2. In the new window select one of the chains and click on "Apply to Files...".
3. In the file selection window select the files.
4. Batch processing starts, displaying various progress informations.
5. After all files are processed, there is a new subdirectory to the one you selected the files from, named "cleaned", containing the processed files.
   

This new directory may not be visible at once in the directory treeview.

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CD Or Playlist, Preparations

Get the size of the playlist

You will probably use some software dedicated to handling sets of audiofiles, that will provide you with all relevant information.

If not, you may control the total playtime by using any available music player capable of displaying the total time.

The file size may be used for a rough estimate. About 0,93 MB for 1 min at a bitrate of 128 kB/s is needed, this size being approximately proportional to the bitrate. Look at the "properties" of the folder containing your files to see the total size.

Adjust the single files to fit to the playlist

Adjust your files concerning, volume, sound etc.. If this goes with repeatedly changing and exporting the file, and if your target file format is a compressed one, it implies repeatedly decoding and coding, thereby degrading the audio quality. Either keep the files loaded in Audacity until the final change has done, or export as WAV or another uncompressed format, and do the compression as last step, after all files are done with, using File > Apply Chain....

• You might check the transitions from one file to the next using a media player at hand or
• import some files, preferably from the start, the middle and the end of the list and do comparative listening.
• If the files are intended for sequential playback in a fixed order, you might align them in one big Audacity file and listen to the transitions there.
• You might import them into different tracks in Audacity, then use the time shift tool to move them along the time axis, thus creating a sequence to be listened to (see the following).

Build a playlist in Audacity

In this way (see last item above) it is easy creating crossfades, altering the order of the files, and control the total playtime.

If the screen becomes too crowded, collapse selected tracks by clicking on the upward triangle at the bottom of the track panel.

However the number of files Audacity (and your computer) can handle at once is limited. To find out, select Help > Run Benchmark.... After some time the results are displayed, and at the bottom you find the number of files playable simultaneously. Using compressed audio does not help, because Audacity converts it to its uncompressed AU-format. To ease processing close other programs.

Instead of the above you may arrange all your songs in two tracks, thus avoiding the mentioned playback limitation. Use a third track for routing/switching purposes.

If Files with different sample rates are involved, see Combining Different Sample Rates. Immediately after the import adapt the sample rate, move the song to the desired place, close the now empty track.

With the time shift tool you can move the songs along the time axis, but also from track to track, so no need for switching tools is given.

If you place the tool on an unselected song, only this song is moved, if you select one track by clicking left of the waveform display, all songs in this track are moved. Avoid shifting songs to the left of t = 0 s.

The first method displays all song names, plays tracks with different sample rates, but the screen gets crowded and the number of songs is very limited. The second method plays a large number of songs, but they have to be of the same sample rate (or must be rendered), and no song names are displayed.

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Re-Vinylize

The following instruction is a modification of the Tutorial in German about using Audacity effects with real-time control. 

1. Obtain an audio file with a lot of hiss, crackle etc.
2. From this extract the noise:
   1. Load this file,
   2. select Tracks > Add New... > Stereo Track (or Audio Track for mono)
   3. copy the loaded file into this new track,
   4. denoise and declick this file as much as possible,
   5. invert it: Select Effect > Invert,
   6. select all (both tracks have to been selected),
   7. Tracks > Mix and Render.
      The last step is the vital step. By "adding" the original and the inverted file all originally identical waves are summed up to zero (thus deleted), and only the noise remains, that by now is only present in one of the tracks.
3. Mix the noise file into any other file:
   1. Import your re-vinylize-file,
   2. press "Play",
   3. adjust the volume of the noise using the gain slider left of the wave display, press "Stop",
   4. Tracks > Mix and Render.

If you want to additionally equalize the file (attenuate bass and treble), do it before adding the noise, else the noise might lose its impact.

There are also free plugins available, look for "vinyl".

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Tips

Clean Cuts

avoid different slopes

In order to get inaudible cuts, apply the following techniques:

• Place the cut into "silence".
• Place the cut at a zero crossing (where the waveform crosses the timeline).
• Place the cut in such a way, that the two ends of the waveform
  join smoothly and show the same gradient (slope).
• Use the Effect > Repair to smooth out remaining differences in the gradient.
  

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Combining Different Sample Rates

Files with different sample rates play in different speeds or not at all, when combined in one track. Proceed as follows:

1. Enter the desired sample rate in the "Project Rate" field bottom left.
2. Select one entire file
3. Do Tracks > Mix and Render, watch the display beneath the track name change.
4. Repeat the last two steps for all other files with a "wrong" sample rate.

Now all files should behave the same.

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Comparative Listening

1. Open two or more files.
2. For files with the same music assure synchronicity.
3. Press "Play".
4. Repeatedly alternate between the tracks by clicking "Solo" on the left of the corresponding Track Control Panel.

For the export of files after using "Solo" see Exporting with "Solo"-Button or "Mute"-Button activated

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Exporting with "Solo"-Button or "Mute"-Button activated

If you export a stereo file while "Solo" is still activated, channel 2 will be muted in the saved file.

If you cannot simply deactivate "Solo", use the Track-Menu to split the file, rebuild it, then deactivate "Solo".

Now both channels are exported as usual.

If instead "Mute" is activated, nothing is exported.

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Preview, Use Of

1. Select the part of the file you want to preview,
2. chose the effect you want to apply,
3. make your settings and press "Preview",
4. repeat the last step, if necessary,
5. if possible, save your settings,
6. close the effect window,
7. select the part of the file you want the effect apply to (or cancel the previous selection, which will cause Audacity to select all),
8. reopen the effect window,
9. confirm the settings,
10. apply the effect by pressing "OK".

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Replace

If sample precision replacements are required, use the following instructions:

The selection bar at the bottom and a label track are used. See [[1]] for a more detailed description of these elements.

For our purposes activate the radio button "Length" and set the selection format to "samples" (this can be done at any of the fields by using the drop-down menu of the field).

• Replace a region with audio from elsewhere.
  Use one of the following methods:
  • Method 1

1. Mark the region to be replaced.
2. Select Edit > Play Region... > Lock. This causes your marking to become stationary.
3. Use the time shift tool, place it outside the marked region, and shift the waveform, until the replacement audio is positioned under the marking (is selected).
4. Press Ctrl-C to copy.
5. Shift the waveform back to the initial position.
6. Press Ctrl-V to carry out the replacement.
7. Select Edit > Play Region... > Unock.

• • Method 2

1. Mark the region to be replaced.
2. Press Ctrl-B to generate a label (name it (say "b"), press Enter).
3. Keep in mind the number of samples shown in the Length field.
4. Go to where your replacement audio is.
5. Select the replacement audio while watching the Length field.
6. Modify your selection until you have marked the exact number of samples.
7. Press Ctrl-C to copy.
8. If your first section has got out of sigth, scroll the display or zoom out to Bring the selection into view.
9. Click into the label "b" (first section gets marked).
10. Close the label track (audio track gets focus with intact selection).
11. Press Ctrl-V to actually carry out the replacement.

• Replace a region in channel 2 with corresponding audio from channel 1.

1. Place the cursor at the beginning of the region to be replaced in channel 2
2. Press Ctrl-B to generate a label (name it (say "b"), press Enter).
3. Mark the region to be replaced in channel 2 (Shift-Click to the right of the current #position, the drag curso to the wanted position).
4. Keep in mind the number of samples shown in the Length field.
5. In the Track-Menu select "Split Stereo Track"
6. Close Channel 2.
7. Press Ctrl-C to copy the remaining channel 1.
8. Undo (channel 2 reappears).
9. Mark the region to be replaced in channel 1 or 2 (Shift-Click to the right of the current position, the drag curso to the wanted position)
10. Close the label track (audio track gets focus with intact selection).
11. Press Ctrl-V to actually carry out the replacement.

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Zooming

Although there is ample help on zooming in the Audacity manual, I include this survey. Because zooming is so vital to remastering, a reminder close at hand cannot be wrong.

• Vertical:
  • Scaling:
    • Move cursor over the vertical axis, a magnifier symbol is shown
    • Click on the axis, to zoom in
    • Shift-click or right-click to zoom out
    • The position of clicking determines the symmetry or non-symmetry of the axis-scaling
  • Size of the display area (not the scaling):
    • Use View > Fit Vertically
    • Draw the bottom line of the track panel, for stereo racks: bottom line of channel 2 resizes both channels, bottom line of channel 1 changes the relative size.
    • Also see Edit > Preferences > Settings > Interface.
• Horizontal:
  • Use the buttons from the magnifier panel
    • "Zoom in"
    • "Zoom out"
    • "Fit Selection"
    • "Fit Project"
  • Use the corresponding options in the "View" menu (here is an additional option Zoom Normal).
  • Use the "Zoom Tool" from the "Tools Panel".

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