De-crackling 78s – a quite simple method

devised by David Younglove,

to whom many thanks!

 

Without any question, the biggest and most chronic problem in playing many 78 rpm records made in Great Britain, is ‘The English Crackle’. That useful term, by the way, is due to Jeff Healey, the renowned Canadian Jazz & Blues musician and connoisseur of 78 rpm records. It is increasingly thought that most British 78 rpm discs would not have crackled in this way when they were new. The irritating ‘bacon frying’ sound associated with playing 78s is now thought to have developed in the records over the years, due to the discs having been stored in unfavourable conditions. As central heating was a rarity in most British homes during the 78 era (roughly 1900 - 1960), discs were subject to an annual summer - winter temperature cycling process. Worse still was the British climate, which tends to be damp at all times. Accordingly, the microstructure of the discs has become degraded, and the surface ‘loosened’. Thus, tiny grains of material protrude from the groove walls, and cause this crackle as the stylus passes by them.

 

That this is the probable explanation, is supported mostly by ‘negative evidence’. For example, occasionally a perfectly ordinary, average looking record, plays very silently indeed. I have a copy of Parlophone R-2127 (Louis Armstrong’s ‘Savoy Blues’, 1927) which plays superbly with no crackle. While on the other hand, I once had a laminated pressing of a Joe Venuti record (these are normally very silent) which crackled horribly. I know that this latter disc had been stored in a garage or outhouse for 30 or 40 years. The protracted time in this hostile environment must have been responsible for the crackle. It follows then, that the silent-surface ‘Savoy Blues’ 78 must have been kept in an optimum environment - though I cannot attest to that fact. That environment logically would be the exact opposite to an outhouse. Inside such a shed, the temperature would cycle between say minus 5 degrees Centigrade in the depths of winter, but with frequent damp spells above  zero, to perhaps 40 degrees C in summer - a British summer also having many damp spells! (Ironically, this is being written on 23rd July 2007, following almost unprecedented rainfall and truly disastrous flooding in many Midland counties of England.)

 

So an optimum environment for storing 78s would seem rather obviously to be a dry one, in which a moderate and even temperature is maintained. There is considerable evidence that this is the case. In North America, there used to be many Record Libraries, e.g. in radio stations, which often contained large numbers of British 78 rpm discs, especially in Canada. Obviously these premises would be air conditioned & maintained at a suitable temperature, in view of the extremes of climate there, which far exceed those of Britain. Yet, with the advent of vinyl, tape, CD &c., when these libraries sold off, their 78 holdings, those British pressings were highly esteemed by the local collectors, who in some cases preferred them to Canadian or U.S. pressings!

 

So I think we can legitimately conclude that our ‘78 problem’ here in Britain is simply due to the weather.

 

Still, having defined the problem, the question remains: ‘What can we do about The English Crackle’ when transferring 78s to CD?

 

There is a digital technique that can help.

 

It was developed by David Younglove. It employs relatively simple software, and only two specialised functions are needed. These are apparently commonplace in this sort of software, so we make no attempt to list such programs. We merely point out that the very ordinary (& cheap) programs already in use here for some years, were found to possess the two required functions.

 

For the record, these programs are Diamond Cut 32 (v 4.01) and Sound Forge 6. The crucial functions are (a) the ability to digitally de-noise a .wav file and retain the residual signal, and (b) the ability to paste a .wav file into another while inverting the data being pasted in. DC32 will perform (a), while Sound Forge will perform (b).

 

The theory behind this technique is almost absurdly simple - once you have grasped it! Actually, it is far more complicated to describe than to carry out - especially if you write complicated old-fashioned English as I tend to do. I will try to become extremely lucid…

 

Also, please allow me to introduce an imaginary friend who asks questions!

 

Question: You have told us you have DC32. Why do you not simply use the ‘impulse noise filter’ provided in DC32 to cut out the crackle?

 

Answer: That filter is extremely effective in many cases, e.g. intrusive noises on tape, or a difficult but short passage on a 78. But, alas, it is not very good for decrackling a 78 ‘all in one go’.

 

Q: Why? Surely DC32 is primarily intended for restoring 78s?

 

A: Yes, it is; and DC32, though old, is excellent & versatile software for working on 78s and I use it for all my audio editing and virtually all my audio processing. This is also because I do not have £20,000 to spend on some CEDAR hardware modules & the associated software. By the way, do you have £20,000 to spend?

 

Q: Er… no! How much did DC32 cost you?

 

A: About £65, several years ago. But can I tell you why DC32 cannot decrackle a 78 side ‘in one go’?

 

Q: By all means!

 

Right. Now I have taken a typical ‘78’ record. It happens to be a typical Columbia record of 1912 with the nominal speed of 80 rpm. I shall now do a bit of simple geometry on this disc.

 

The first groove on side 1 begins 12.1 cm from the centre of this disc.

 

So we may assume an effective diameter of 24.2 cm & hence a circumference of 24.2 = 76.02 cm.

 

Having used 80 rpm for the transfer, we have 80 ÷ 60 = 1.33 revolutions per second.

 

Thus the groove velocity on the first turn is 76.02 x 1.33 = 101.1 cm/sec.

 

But at the end of the side, the groove is only 5.2 cm from the centre of the disc.

 

Thus the groove velocity there is only 10.4 x 1.33, i.e. 43.45 cm/sec.

 

So from the start of the disc, with each rotation, the groove velocity will decrease in a linear fashion (assuming a constant groove spacing), from its initial velocity, to only ~42% of that value by the end of the record.

 

No wonder ‘old 78s’ sound duller towards the end. The same amount of ‘information’ has to be squeezed into less than half the space by the end of the disc!

 

Equally, the ‘crackle’ of a 78 is due to the granular structure of the material from which it is pressed.  And if we assume that the ‘grain size’ of this material is uniform (a generally permissible assumption), then simple geometry informs us that each ‘crackle’ will be, at the end of the disc, at least twice as long in duration as it was at the start. But it will also be of lower amplitude, as the velocity of the groove is lower & so the ‘crackle’ registers less on the stylus. It goes without saying that any de-crackling process we carry out must observe this progressive change in crackle duration/size.

 

Unfortunately, DC32 cannot do this. You can only set the parameters for crackle removal at the start of the disc. After some time, as the groove velocity gradually falls, the duration of the crackles will increase, and so another setting in DC32 is required.

 

Q: Can you not simply process the 78 in a number of sections, changing the settings as you progress through the disc?

 

A: Oh yes! That is quite easy - though rather time-consuming -, and I frequently use that approach on ‘one-off’ transfers. But there’s another very significant thing: DC32 is only really effective at decrackling a certain type of sound, so the content of the record is important.

 

Q: But surely, all 78s are much the same in content?

 

A: [Prolonged laughter] Whatever gave you that idea? I don’t know how CEDAR works it, but the impulse noise filter in DC32 is highly influenced by the material on the disc. Audio which contains a lot of slow-rise, low frequency, legato music is quite easily decrackled in a small number of sections by DC32. But I’m afraid that sopranos are a perfect beast!

 

Q: Here, steady on! I like sopranos!

 

A: I dare say: but their high notes look like this to a computer program:

 

soprano

 

and all those cycles, as you can see, are contained within the time period 7.3041 to 7.3412 seconds, a duration of just under four hundredths of a second; so you see the problem?

 

Q: No; what is it?

 

A: Quite simply, that so many ‘events’ in such a short space of time is likely to confuse the decrackling function of our program. Mainly, the decrackling function is likely to regard each and every one of those sinusoidal excursions as… a steep-rise crackle! And it will therefore try to remove them, which naturally causes catastrophic distortion in the resulting output file.

 

Q: I thought computers were supposed to be extremely good at this sort of simple, quick, repetitive task?

 

A: I’m sure they are; as long has one has spent maybe £20,000 on a CEDAR outfit which tells them what to do.

 

Q: Can the technique you are describing ever cater for such things?

 

A: In one sense it can, to some extent! But I must confess that I have played a trick on you, because the wave-form above is an extreme case. Such a wave-form would need no decrackling. The amplitude of this soprano’s high note (four-hundredths of a second of Joan Hammond, actually) would by far, over-ride any crackle on the 78 rpm disc. The ‘difficult crackly bits’ would be the pauses or silences between various sections of the singing.

 

Q: Pray proceed with your explanation. I am greatly interested!

 

Thank you for your courtesy! Here we go…

 

As we play a 78, there is a sequence of objectionable ‘crackles’. Now, leaving aside the music:  suppose we could make a copy of each of these tiny crackles?

 

It would look something like this:

 

crackle1

 

Each crackle of course is unique, having its own amplitude and duration, depending on the size & prominence of the particle in the groove wall that had caused it.

 

Then, suppose we inverted these impulses? So that each of them was equal & opposite?

 

We would then have this:

 

crackle2

 

Now comes the clever bit! If we could put this ‘equal & opposite’ signal back into the original sound file, would not each impulse cancel out the original from which it was derived?

 

Pictorially, we are looking at the following:

 

crackle3

 

If the positive and negative excursions shown above are played back together, they will cancel out, and the result should be zero.

 

And above all, the inconvenient factor that crackles gradually get longer (though of smaller amplitude) as the disc plays through, is automatically taken care of. Because each individual crackle is nullified by an exactly opposite counterpart derived from it, no matter whether it came from the beginning of the disc, where crackles are short but of high amplitude; or from the end, where they are of low amplitude, but more than double the duration.

 

So let us now begin work on Columbia 2129. It is by the St. Hilda Colliery Band; they won the Band Championship in 1912; a selection from ‘William Tell’, arranged by William Rimmer, and occupies both sides of the disc.

 

We will use the start of side 2 for our examples. This is because, curiously, side 2 is more crackly than side 1. We know that Columbia recorded - nominally - at 80 rpm at this time, so we played the disc at that speed. A .0035” TE stylus in a Shure M44 cartridge worked best for this disc - perhaps a slightly larger size stylus than one might have expected, but it seemed to give a good ‘solid’ underlying sound.

 

Here is the appearance of the second side on the screen of DC32.

 

tell2orig

 

You will note that there are a number of clicks.

 

Q: What is the difference between a small click and a large crackle?

 

A: I knew you’d ask that! Well, I don’t know whether there is a proper definition of when a large crackle becomes a small click; after all, one might say that a small crackle is a very small click? What they do have in common, of course, is that they both rise steeply, both are objectionable, & we want to get rid of them. A rule of thumb I use, is that if you get a distinct visible spike, as above, then it’s a click. The crackles are really small, and not usually apparent unless you zoom in quite a lot. In any case, it is better to remove these distinct clicks manually. There aren’t very many of them on this side, so it won’t take long. And we want to concentrate on the tiny crackles, and optimise our settings to deal with those, not huge great clicks.

 

Here is the file after manual declicking. There are one or two clicks left, but what the heck!

 

tell2declick

 

Q: You are working in stereo, or at least binaural mono. Why?

 

A: Because the crackles are scattered at random around both groove walls. If we put the file into mono. at this stage, some crackles will be masked, and some will cancel each other out - but many will just be reduced  a bit & lurk around & not be eliminated. We want maximum ‘visibility’ of crackles at this early stage.

 

Click here to hear the first ~30 seconds of an mp3 of the declicked file above.

 

Now comes the first critical stage of our procedure. In DC32 (or whatever program you are using), we apply a severe digital denoising to the above .wav file - but only ‘save the residue’. The original file would sound dreadful after this sort of denoising; but we’re not going to use that. We are just pulling out from it as much noise as we can, for use later on. This noise consists of rumble, waffle, hiss &c., and the crackle, which is what we’re interested in.

 

Here is a picture of the extracted noise:

 

tell2noise

 

Click here to listen to the the first ~30 seconds of it.

 

The second critical stage is to severely decrackle the above file. In DC32, this means using the ‘impulse noise filter’ with very high settings.

 

Having done this, we ended up with the following file:

 

tell2intonoise

 

It doesn’t look much, does it? It’s actually nearly all hiss, as you can hear if you click here to listen to the first ~30 seconds of it. But it is this innocuous looking (& sounding) file which will enable us to isolate the crackle we need!

 

We now leave aside DC32 - because it does not possess the critical function we need right now. But Sound Forge does have the ability to paste-mix and invert at the same time, which is what we need to do.

 

So, we come to the third critical stage. In Sound Forge (or whatever program you’re using that can paste-mix & invert), open file 3 above - the whole noise.

 

Then, also open file 4 above, the hiss. Copy this file onto the clipboard & then close it down or minimise it.

 

Then, paste-mix file 4 INVERTED into file 3.

 

The noise - hiss &c - will cancel out the noise in file 3, and leave just the crackle! Click here to listen to the first ~30 seconds of the ‘crackle file’. Amazing, isn’t it? It’s just crackle & nothing else.

 

Finally, copy this crackle file (you don’t actually need to save it) onto the clipboard, and then paste-mix it, INVERTED, into file 2 - i.e. the original audio file.

 

Each crackle should be equal & opposite to those in the original file, and will cancel them out. You will end up with a decrackled file - here it is:

 

tell2decrack

 

It doesn’t look very different; but it sounds different. Click here to listen to the first ~30 seconds of it. H’mm, I notice that one click has survived about three-fifths along the left hand channel - but again, what the heck.

 

Now to put it into mono., which will clear up a lot of rumble & waffle.

 

tell2decrackmono

 

Click here to listen to the same ~30 seconds.

 

That’s the essential Younglove Process. You could then put on some suitable equalization which would increase the presence – bring the sound forward, &c.

 

The final file sounds a lot better than it did to start with, and we haven’t done any digital denoising on it at all. That option remains. Personally, I hate digital denoising.

 

 

N.B. This page was written some time ago, and there is now available relatively inexpensive software such as Izotope RX4, which actually does go forward into the file and analyses what clicks and crackles are approaching, and deals with them appropriately. The Younglove System is nevertheless still extremely useful, and retains its elegant simplicity and effectiveness.

 

Also, this 78 was transferred with the wrong equalization to start with, as we played it through an amplifier with the RIAA (LP) curve. Mechanical (acoustic) recordings should be played ‘flat’, and only then worked on. We have since adopted this practice – there are references to it elsewhere on this web-site, including phono cartridge pre-amplifiers that offer not only a flat response, but also switchable EQs for Western Electric, Blumlein & other playback profiles.  

 

 

Page written 23rd/24th July 2007.

Revised & re-formatted 18th December 2015.