Needlework – Digitize your LPs and cassettes with Audacity

The good old vinyl LP is currently experiencing a revival – you will even see hipsters listening to cassettes – but it is not a good idea to expose these treasures to the ravages of time: Audacity helps you archive analog music in a digital format on your hard drive.

Analog

In their day, records and cassettes were undoubtedly milestones in the development of music media. Many of us still have shelves full of these now archaic sound storage media in the attic or basement. Whereas vinyl LPs are seeing a growing community of friends flocking back to the fold, the miniature version of the reel-to-reel audiotape has shrunk virtually to irrelevance.

You might already have replaced many of your old treasures with CDs, but some old recordings mastered in professional recording studios were probably only ever available on LP. Certainly private recordings, demos, and local productions of your school band are consigned to the medium of their era. Therefore, it is important to preserve these treasures against decay.

Professional

The easiest way to convert your material to digital is to connect an analog player directly to a digital recorder. Quite a few all-in-one devices on the market that play records have a memory card slot and often even a cassette drive. The quality of the hardware components are typically entry level to middling, and the ability to influence the output is usually around zero.

These limitations often result in unacceptable quality, so it makes more sense to connect your turntable or cassette deck to the sound card of a PC or a USB adapter, which ideally often also includes a matching preamplifier (see the "Connection" box).

For recording, you also need sound editor software, such as the open source tool I use in this article, Audacity [1]. Audacity comes with both basic recording tools and functions for restoring and optimizing the quality of a recording.

Recording in Progress

After launching Audacity, first select File | New Project and click to save. Next, click the Record button in the toolbar and start playback on the cassette deck or lower the stylus onto the LP. In principle, you can now grab a cup of coffee while you wait for the recording to complete. However, you might want to take the time to watch the two green level indicators at the top right: If they deflect too far to the right and turn red, you either need to reduce the signal intensity from the amplifier or use the slider in Audacity and then restart the recording to avoid distorting the sound.

In general, you need to do this only once, unless you change your setup. To help you find a peak level, it makes sense to listen to particularly loud sections up front and then record them for test purposes. In this way, you can prevent distortion without having to discard the entire side of an LP. When you are done (Figure 1), you can click the Zoom In and Zoom Out icons in the toolbar to enlarge the recording and check certain areas in more detail.

Figure 1: After recording, zoom out once again for a general overview.

Spring Cleaning

As analog, mechanically scanned recordings, LPs deliver noise in addition to the payload signal. Frequently played records pop, crackle, and distort the signal because of dirty grooves. Cleaning with an antistatic brush before playing helps, but other tricks can trim an old recording for a cleaner sound (see the "New for Old" box).

Scratches will be unimpressed by all of these efforts, and the best cleaning will not prevent the resulting pops. Pops are visible as short spikes in the view window; the levels climb steeply and stand out clearly in the wave plot. To correct, select the appropriate section with the mouse and zoom the view with the Zoom In icon in the toolbar, by selecting View | Zoom In, or with Ctrl+1 until the scratch is shown as a single pulse (Figure 2). This works best using View | Zoom to Selection to fit the highlighted area to the view and dragging the markers even further with the mouse.

Figure 2: A scratch is clearly visible with extreme zoom.

Now use the Effect | Fade Out function to iron out the scratch virtually. Applying the effect once only will not knock the unwanted peak flat straightaway; as a rule, you need to repeat the procedure several times, but when you are done, the pop and crackle in the recording should disappear completely. Be sure to interrupt your work occasionally and save the project to avoid data loss.

Alternatively, Audacity offers a semi-automatic scratch removal tool; just select Effect | Click Removal (Figure 3). A little tuning of the default values usually results in clearly audible improvements, but the results can hardly compare with the manual scratch removal method described first, because Audacity lets too many scratches pass. Excessive values can even affect the sounds of the percussion section if the click removal algorithm is overly rigorous, so you should be careful when using this function.

Figure 3: Audacity can smooth out scratches in a semi-automatic process, but the effect has its limitations.

Because an LP is an analog recording, automatic routines will always find life hard. No automatic recipe can remove the typical crackle of vinyl. The Effect | Noise Reduction option built into Audacity will achieve moderate improvements, but don't be surprised if the program first asks for a noise profile: The spectral composition of noise is so diverse that it is difficult for Audacity to assess it correctly. Mark a small noisy area in front of or between tracks, and click on Get Noise Profile. Audacity then stores the profile in the project. Next, select Edit | Select | All to select the entire recording on which to apply the effect.

Do not delude yourself: The record will not sound as fresh is it did when you first picked it up from the store. Crackling is far too inhomogeneous for this method; however, you will achieve far better results when processing audio tapes, because their noise is created by the low speed of the magnetized tape and has a much smoother frequency spectrum.

Sound Development

In addition to noise removal, Audacity can digitally equalize the frequency response. A rumble filter, which minimizes the low-frequency noise of the turntable drive is a typical example. Under Effect | Equalization is a settings window (Figure 4), in which you can select from several equalizer profiles. Rumble, for example, is a high-pass filter that attenuates low frequencies. If the preset 100Hz swallows too much bass, you can change the curve by dragging it with the mouse to find a workable compromise.

Figure 4: A Rumble filter is useful if the amplifier does not have a high-pass filter.

The Recording Industry Association of America (RIAA) standardized the distortion of the frequency response caused by nonlinear movement of the stylus across an LP; many, but not all amplifiers compensate for this. To improve the audio recording, you should take a look at the RIAA equalization curve [2], which reduces the trebles and boosts the bass. What sounds better in the end is up to you. The standardized frequency adjustment does not necessarily represent the best choice.

Since the mid-1960s, Dolby Laboratories has developed various procedures to get rid of tape hiss that have consistently improved over the decades. Noise contains especially high frequencies, so the signal in this area is raised and lowered during playback, depending on the input level, which also reduces noise. Dolby SR (spectral recording), used in studio work, is capable of reducing the noise level by up to 25dB. The equalizer is also interesting for tape recordings. A cassette recorded with a Dolby method [3] skews the frequency response when played back with a Dolby-enabled playback device. However, Audacity does not offer a profile for this purpose. For the appropriate standards, see a discussion of Dolby noise reduction online [4].

Divide and Conquer

On an LP, but not a cassette, you can see the breaks between tracks with the naked eye. However, when you digitize an LP, the breaks vanish, giving you an album of a single file. Thus, the recording needs to be split into individual tracks.

The timeline above the recording view helps you find the breaks. If the album cover lists play times, you can easily calculate where you need to insert your virtual knife. Simply click on the view and drag while holding down the mouse button to expand a section corresponding to the desired track. Drop-offs in the recording level also give you clues, but they can be misleading, especially with live albums.

In practice, the best approach has proven to be starting at the end of the recording. It is easier to listen to just a few seconds than a whole track, just to keep the fade-out at the end of the track. Once you have found the end, drag the opposite edge of the highlighted area to where you think the track starts. You can find the exact starting point by briefly listening in and moving the marker as needed.

Once the selection fits the bill, export the current title to a standard format for audio players. File | Export Selected Audio opens a file dialog that saves the selection as an uncompressed WAV file by default. At bottom right, you can select additional codecs, such as Ogg Vorbis and MP3. When you select these options, additional options appear, such as Bit Rate Mode and Quality. If you prefer to use an exotic encoder, choose (external program) instead of a listed codec, where you can specify a custom command to be executed on the command line for an external application.

Rolling up the recording from the back is also a very convenient way to split live albums without losses. For the penultimate title, just drag the end marker of the last track forward with the mouse to the beginning of the new track. In this way, the start marker for the first track you stored becomes the end marker for the new track.

Secret Code

Formerly, digital players obtained information about the artist, album, and track from the file name. The related album cover was only displayed if it was provided in the folder. These days, details of the recording are saved as metadata stored directly in the audio file. When exporting to such formats, a corresponding editor pops up (Figure 5); you then can add information such as the title, artist, album, release year, and more.

Figure 5: The metadata editor is sufficient but cannot compete with specialist tools.

By default, the dialog only lists a couple of tags; if you want more, you also need to have a good knowledge of metadata standards for the desired format. Additionally, the editor is not particularly useful if you want to edit an entire album. Tracks exported from the same project appear over and over again with the same tags as the file saved previously. In many cases, it makes sense to export the recordings without the metadata and add the metadata later with a specialist tool such as EasyTag [5].

Conclusions

With relatively little effort, you can rescue LPs and tapes as MP3 or FLAC files for a new life in the digital world. Some caveats still apply; for example, the metadata editor is not always practical. The wxGTK basis of the program is also noticeably ugly in some places. The shift from Gtk2 to Gtk3 occasionally causes display glitches.

Alternative candidates are few and far between. EKO [6] and similar simple sound editors are of limited use for this job. Only KWave [7] offers functionality similar to Audacity; otherwise, you will be hard pressed to find a better audio editor in the repositories.