Sample workflow for tape digitization
From Audacity Development Manual
This workflow does not at any stage necessitate the saving of an Audacity project (though you may wish to do that if you need to interrupt your work). Your final goal will be to export WAV files for CD creation or other file formats which might be more suitable for your needs.
While all of the processing in this tutorial is carried out using Audacity, some users may prefer to use alternative software for specific sub-tasks like noise removal and the removal of clicks and pops (Audacity's Click Removal may not give as good a result as other software).
For more details of the steps involved in this workflow please see the tutorial set Copying tapes, LPs or MiniDiscs to CD.
- Audacity Settings
- Check/adjust the azimuth settings
- Clean the heads
- Retension the tape
- Recording levels
- Raw master backup
- Remove DC offset
- Reduce tape hiss and high frequency noise
- Place the song labels
- Silence the inter-track gaps
- Fade Ins/Outs
- Adjust Label positions
- Track names
- Advanced labeling techniques
- Amplitude adjustment
- Export a set of WAVs
- Export labels
- Alternative software
- Consider starting out with some tapes that you care less about, this way you will not need to go back and repeat important earlier transcriptions that you made.
- Start with a recording that you are very familiar with; your first goal will be to ensure that you have as perfect a digital copy of the material as possible.
- Clean-up steps are optional and need only be applied if your recording requires them.
Work with Audacity set to a project rate of 44100 Hz and 32-bit sample format (these are the default quality settings). You may use 16-bit if you prefer; it will give smaller working file sizes but you may lose a little quality in some of the processes. Export WAV files at 44100 Hz 16-bit PCM stereo, the standard required for burning CDs; this will also produce WAVs which are accepted for import by iTunes (and most other music player software).
Check/adjust the azimuth settings
Azimuth is the angle of the magnetic gap in the tape head relative to the tape. This should always be 90 degrees, but in practice most cassette decks fail to maintain accurate head position, hence the azimuth of cassette recordings routinely varies. Pre-recorded tapes are much better, but not entirely immune to azimuth variation.
Misaligned azimuth routinely causes degradation of high frequencies and signal to noise ratio.
See this Wiki page for advice on how to adjust your azimuth setting.
Clean the heads and pinch roller
Most deposited oxide goes onto the pinch roller. The more oxide there is on this roller, the less able it is to remove and hold loose oxide from the tape, and thus the more oxide gets deposited on the head.
A dirty pinch roller has less friction, and can occasionally result in tape slip, degrading playback quality. This is especially true for 8 track tapes, where tape slip is a real issue.
All types of tape deck that use a pinch roller should have the roller cleaned occasionally. Microcassettes and picocassettes don't use pinch rollers.
Retension the tape
Tape that has been stored unplayed for a long period of time can benefit from having its tension evened out prior to making the playback for recording capture.
To do this simply use the fast forward to advance the tape to the end and rewind to the beginning (but take care with this if you a working with a low-grade deck that has a poor, or no, braking system as this can cause the tape to come off the spool). If you have plenty of time you could instead just play the tape at normal speed and then play the second side before making the actual recording.
Read this page about making a test recording then make a test recording of portions of the tape (or even a whole side) so as to check the levels. It is important to avoid any clipping during the recording! Try to aim for a maximum peak of around –6 dB (or 0.5 if you have your meter set to linear rather than dB).
|Enlarging the Recording Meter Toolbar by clicking and dragging helps with this task; you should read this section about resizing the Meter Toolbars.|
Record both sides into the project prior to doing the processing. You can either Stop the recording after the first side using the button or SHIFT + R) to restart recording when you are ready. Alternatively you can pause by pressing the button (or use ) at the end of the first side and then press the button again once you are ready to record the second side.and then use (or use
After recording you may find it helpful to zoom out to display the entire recording in the Audacity window.
You may prefer to work with a single side of a tape at a time as that gives a smaller working set.
Raw master backup
Export a single WAV for this recording at 32-bit float (not 16-bit).
Retain this WAV file as a maximum quality "raw capture" file that you can import back into Audacity later to start over (if you damage the project while working on it).
Remove DC offset
DC offset can occur at the recording stage so that the recorded waveform is not centered on the horizontal line at 0.0 amplitude. If this is the case with your recordings, see the Normalize page for how to use Normalize to remove DC offset and how to check if your Windows sound device can perform this correction automatically.
Reduce tape hiss and high frequency noise
Use the Noise Reduction effect's Get Noise Profile to obtain a noise sample from either the lead-in grooves immediately before the music starts, or from a lead-in between tracks. The length is not important but, typically, it will be less than a second; what is important is that you have a true representative sample of the noise without any audio signal at all (such as a very quiet fade lead in). Try amplifying the sample and audition it to ensure that no real audio signal is present. If it's OK, undo the amplify, then re-apply the Noise Removal effect with these recommended settings:
- Noise reduction - no more than 12 dB (9 dB is a good guideline)
- Sensitivity - 6.00
- Frequency smoothing (bands) - no more than 6 (3 or lower is a good setting for Music)
Noise reduction is always a compromise because, on the one hand, you can have all the music and a lot of noise and, on the other hand, no noise and only some of the music. Try different settings on the "Noise Reduction (dB)" slider until you get the best compromise.
Place the song labels
Mark the approximate label points - click in the waveform at the approximate point between the tracks on the album, press CTRL + B then ENTER. Don't forget to insert a label at the beginning for the first track. Alternatively you can mark a label point while recording (or on playback) using CTRL + M ( COMMAND + . on Mac ).
Silence the inter-track gaps
These are rarely truly silent so you may want to replace them with silence by selecting the gap and using CTRL + L or the Silence Generator effect. Edit the inter-track gap as desired to around a maximum of 2 seconds; you may wish to use a shorter gap or even no gap at all for some recordings.
|By default CD burning software almost always adds a 2-second gap between tracks. Check for any options to turn this off, for "gapless burning" or "Disc-at-once (DAO)" that you can enable.|
You may wish to more cleanly fade-in and fade-out the song beginnings and endings by usingand . Normally fade outs should be longer (typically a few seconds), and fade ins, if required, quite short (typically a fraction of a second).
Consider usinginstead of the linear Fade Out. It applies a more musical fade out to the selected audio, giving a more pleasing (more "professional studio") sounding result.
You may also get a more musical fade-in by applyingmultiple times to the selected audio; three times is a good guideline. This will produce a shaped, curved, fade rather than a linear one.
For instructions on how to do this please see the Keyboard Preferences page in the manual.
Adjust label positions
If you are using a 2-second gap, adjust the label position as desired to be 0.5 seconds before the start of the next track. To move the label, drag it by its center circle.
Edit the labels for the song names - we suggest using "01 First Song Name", "02 Second Song Name", and so on as this helps keep them in the right order for CD production or loading into iTunes. You may find that changing the zoom level will help you with this task; you can advance to the next label by ensuring that the focus is in the current label then using TAB.
If you wish you may instead automatically prefix named tracks with a sequential two-digit number.
To do this, in the "Name files" section of the Export Multiple dialog select the radio button.
Advanced labeling techniques
Normalize the amplitude of the recording; either do each track of the recording individually (especially if the tracks will be randomly played from a library containing many different styles of music) or, do the whole recording at once (which will work fine if all the tracks have the same average volume). Useas the last editing step, setting "Normalize maximum amplitude to" to around -3 dB or similar, to give some headroom below the distortion level. The Normalize effect can be set to either:
- Adjust the amplitude of both stereo channels by the same amount (thus preserving the original stereo balance), or
- Adjust each stereo channel independently (this can be useful if your equipment is not balanced).
The Compressor effect reduces the dynamic range of audio. One of the main purposes of reducing dynamic range is to permit the audio to be amplified further (without clipping) than would be otherwise possible.
Compressor makes the loud parts quieter and (optionally) the quiet parts louder. It can be very useful for listening to classical music in a car. Such music normally has a wide dynamic range and can thus be difficult to listen to in a car without constant volume re-adjustment.
Export a set of WAVs
Use dither noise will be applied by default to cover any defects (clicky noise) that may result from the conversion from 32-bit to 16-bit. Advanced users can change the type of dither, or turn it off, in Quality Preferences.to produce a set of WAVs for each track on the tape at 44100 Hz 16-bit PCM stereo. Audacity will down-sample on export from 32-bit to 16-bit. Shaped
In order to facilitate later retrieval and use, place all the files for a particular album in a specifically named folder for that album.
Some users advise a final step of exporting a file containing the labels. UseThis produces a text file that you can later re-import using should you wish to re-edit from the raw capture file that you backed up earlier in the workflow.
Backup your exported WAV or MP3 files - you don't want to lose all that valuable work and have to do it all over again, do you? Computer hard drives can fail, destroying all data.
Ideally use a dedicated drive (1+ TB external magnetic drives are convenient and economical), or upload to an online (cloud) storage service to store the WAVs or MP3s. Better still is to make two copies on different external devices and even better is to hold an online backup as well as the local copies.
You may want to create a taxonomic file structure - for example each album can be stored in its own folder (named for the album) within a folder named for the artist (or, perhaps, composer for classical music) to make searching and retrieval easier.
- GoldWave: Though nominally not free it is a top class, free trial click remover as well as an excellent alternative audio editor. Its click removal is an effect, just like in Audacity, and there is a "Smoother" effect for broad unwanted noises and an excellent "Noise Reduction" effect for steady noise. The trial version limits you to a hundred or so commands per session, and a total number of several thousand commands before it expires, but if you export from Audacity as 32-bit WAV and just do Click Removal in it, you should be able to declick several hundred records for free.
- Gnome Wave Cleaner: Only for Linux users. Digital restoration of CD-quality audio files. Dehiss, declick and decrackle in a GUI environment. It can also automatically mark song boundaries if required.
Hiss and noise removal
- DeNoise: This is a (paid for, but with a free-trial period) third-party tool effective at removing noise and hiss. Some new users may find it intimidating as an entry level tool. Users report that settings normally have to be reset for each recording to optimize the noise removal thus making it difficult to use in a semi-automated way.
Please see Chris's Dynamic Compressor for a popular alternative compressor which may be downloaded for free. It works by trying to even out abrupt changes of volume by employing "lookahead" (this attempts to anticipate volume changes by starting to apply compression before the volume rises to the threshold level). It has options to soften the softer audio and invert loudness.
> See also Recording from Cassette - article in the Audacity Wiki