This can be done better.

No doubt about that. This is not a studio job, but DIY. All we have to hand is a Revox tape machine from the 1970's, a mid-range Sony record deck, and a bunch of material some of which is nearly 40 years old. The discs are scratched and full of dust. The tapes are shedding their oxide like leaves in autumn. Help!

We also have a bog-standard home computer. And we've used a handful of freely available software tools to make some sense of this. Their reduction of Noise can be patchy. Sometimes, especially with percussive sounds, those of you with headphones might hear the odd squelch or whisper (where the crackling or popping has been removed), or the tonal quality may in some other way not be quite right. This affects, for example, conga sounds and keyboards. In time the quality of recovery will rise, and this is just the first attempt.

(Note 20/02/2009: since this was written, all tracks have been remastered in Cool Edit Pro)

The tools are -

Audacity
http://audacity.sourceforge.net/

Free sound recorder/editor from Sourceforge. Good piece of Open Source work. Can't say I understand all its little ways, and the Equalizer is fiddly (I prefer old-fashioned sliders), but it was the focus for this project.

Depopper
http://www.droidinfo.com/software/depopper/

Handy little bulk depopper/decrackler. 30 day trial, $18 to buy. Take a WAV file or files, bung it/them through Depopper and the big clicks mostly vanish as do some of the small ones, without taking out too much top. This can take a half-hour for an album. You might find you need Audacity later to trim what's left. Noise removal for cassette tape hiss rather than low-end rumble. Particularly useful to balance left/right at an early stage - my damn deck favours the left channel.

Polderbits
http://www.polderbits.com/

Sound editor/recorder. 14 day trial, $29.95 to buy. Multi-purpose. Cut albums into tracks, add that bit of EQ (sliders, though not configurable) to tracks that need it, and save as MP3. Audacity uses the Lame plug-in for MP3, which is OK. Just wish one of them had a 20-band configurable sliding equalizer.

Nero Burning ROM
http://www.nero.com/en/index.html

The tracks on this site are MP3. Would you want to download an album's 400MB WAV file? But for yourself, you'll want to burn the finished WAV articles to audio CD/DVD (and the MP3 files to data CD if that's how you store them). I happened to have Nero already so used that, burning to CD-R rather than RW.

Something like Adobe's Audition or its predecessor Cool Edit Pro would make all this a breeze, but we're cheapskates and we don't mind fiddling about in the small hours.

The computer is a 1.6GHz AMD bargain box from a local company. Critically, it has enough disk to store the huge .WAV files generated (averaging 45MB per track at DVD quality), and a bog-standard sound card, a Soundblaster Live 5.1.

Luckily, the Sony deck has its own pre-amp, so it can be plugged directly into the sound card, via a phone-to-minijack adapter. Otherwise you will probably need a pre-amp, and they cost. Watch out for pre-amp earth hum. Those with an external power supply should be relatively hum-free. But Audacity does give you a RIAA profile for EQ on record, which just might (haven't tried it) do something to make up for the ghastly results of trying to record without a pre-amp. Try to keep everything on the same power strip.

The tape machine is a Revox A77 MkIII. Word of warning. If you send one off for repair swathe it in bubble-wrap, foam, carpet, cushions, whatever, put it in a box, and put that box in another box suitably insulated with foam or other packing material. Otherwise the machine will break when the courier company drops it, which they certainly will.

And then - here are some standard steps. You might find you want to do them in a different order or not at all, for tracks that are already in reasonable shape, or where compression turns everything to mud.

Clean the deck, check the stylus, again. Service the Revox, demag the heads, generally clean-up that dropped-off oxide, and align. If the heads are just about dead get it serviced with perhaps a relapping of the playback head (approx £40) or even replacement of the head(s) at approx £180 each. Ouch.

Clean the vinyl. There's a great deal on the Internet about how to do this, about what residue is left by what method etc. Personally I'd use just a disc brush. Where I experimented with other solutions all I did was wash the dirt lower into the grooves. You can use the software later to fiddle with the crackling and pops, but there's not much you'll be able to do about the physical crack made by some twit with a beer glass in 1982 (except hope no-one notices. Which they might, when they are hopping about to the beat, which skips, and they all end up on the floor).

Prepare the tapes. Some like to bake them, to recover some lubricant and reseat the oxide. Never do this with acetate tape, and only as a last resort, for polyester tapes of the mid '60's to early '80s. My experiment reveals this can work, but not always. 4 hours at 130 degrees Fahrenheit in a domestic oven (not a great idea - watch out for magnetic fields), turning every hour. Temperature checked with a meat thermometer. No permanent damage yet observed. Either a modest temporary improvement or none at all. Again, more info on the Internet. At least store them tail-out and smoothly wrapped.

Step 2: the first (and second) WAV file

Disc. Plug the record deck's phono output (or separate pre-amp if you have to use one) into the sound card's Line input via the phone-minijack adaptor.

Tape. Plug the tape desk's Line output into the sound card's Line input.

Record. I use Audacity for the first step, though just about anything (Polderbits, or whatever comes with the sound card) will do, to get that first dirty WAV file. Though Audacity is a bit fiddly, and I seem to get a view of the level only by pressing the record button, when I'm not actually ready to record yet. (Perhaps Pause is the answer...). Still, you can open another Audacity session to do the actual recording, when you've got the level right in the first one. Get the Line input level as high as you can without clipping. Export the WAV file. My sound card allows DVD (48000) sampling quality. I use that until the final save-as-MP3 step, where I go down to CD stereo quality (44100).

Depop. For tracks from very crackly/poppy discs, run Depopper. Select one or a group of input files. Set the Big Click level lower (say to 55) for noisy discs; otherwise stick at the default of 70. I use the Normalise function to balance channels. Depopper by default will save the WAV file(s) under a new name - the original plus an extension of _NEW. Look out for squelching/whispering sounds where noise has been removed, and you might have to add some top later.

Step 3: fiddle

1. In Audacity, check for major oustanding spikes that Depopper missed in the saved file. Major spikes/clicks will affect overall compression and stop you amplifying later. I envelope or compress them out. Compressing them out can be with or without compensating gain. I try just to narrow down the selection to the spike itself and compress it to the level on either side. That is usually a 10db reduction but can be as high as 15db.

2. Still with Audacity, have a go at removing further noise. (In my case, the rumble of the pulley-driven record deck). Select a noisy bit, say 2 seconds at the beginning of the track. Make that the Noise Removal selection. Apply that Noise Removal at low level (fully left) to the bulk of the track and at high level (fully right) to spaces between tracks and at the beginning and end, to flatline. Careful you don't wash out useful top or bottom by removing the frequencies that Audacity identifies as Noise, though it does appear reasonably intelligent. But you may need to adjust EQ later to compensate. What you might notice is - squelching again (as with Depopper), especially of upper/top frequencies, a slight squelching noise left by Noise Removal. If that's too obvious, and if you don't like it, you might try reducing the level of Noise Removal, or using a different piece of noise as the Noise Removal selection. (Note to the developers: it would be nice if Audacity had an even lower level of noise removal - another notch to the left - for finer tuning).

3. My favourite bit - compress the whole track! This is obviously a terrible idea as a rule, ruining those delicate dynamics, but with material as old as this it does wonders in some cases for what you can hardly hear any more. I compress the lot by 7db generally, enable compensating gain, and sit back admiring a fatter waveband.

4. Amplify, if possible. After all, we want to squeeze the umpteenth ounce of volume from this ancient stuff, don't we? But you might find that the compression-with-gain has raised the track already to its limit.

Save the WAV file! What a blessing that we have massive hard-disks nowadays.

Step 4: finish

1. Polderbits kicks in, to cut up tracks (if the WAV file is, say, a whole or half album), adjust EQ, and save as yet another WAV file, or batch of them. You may need to adjust track start/end positions manually. Theoretically, you could at this point also quite simply save the track(s) as MP3, but there's one last step that no-one in their right mind would take, but I do anyway.

2. Compress the lot again! Yes, being a radio fan, I just love that compression. Quite often, back in Audacity, I take the Polderbits output WAV file(s) and compress them with gain to the limit. Make that waveband fat! Save again!

3. Back in Polderbits, load and save as WAV and MP3. This is where I cut down to match the media, CD stereo (44100).

4. Burn the WAV file to an audio CD. Put the MP3 versions, well, here.

(5. Remove all those temporary WAV files.)

There is a lot of toing-and-froing in this. Manufacturers of these products may say that theirs can do it all in one place. But having played with them, they're not always the best for me in all departments. So, this is just a personal preference, and you may well choose differently - or choose Audition/Cool Edit Pro if you're feeling rich. But that is how these old tracks were recovered.

Note (02/04/05): disregarding all that, we 've just ordered a copy of Cool Edit Pro for Dr Hindsight, to keep him quiet... he says the de-clicking is better with CEP. That means a second entire review of ALL the tracks... O well, keeps him in work.