With high definition, you’ll be able to experience sounds which have only been heard up till now by people who were either present at Callas’s recording sessions, or who had access to the unique

master tape,’ says Allan Ramsay, one of the team of engineers responsible for this remastering of all Callas’s studio recordings. ‘And digital editing software has become so sophisticated that we can correct problems which were insoluble even a few years ago. The listener will experience something as close as possible to the actual recording sessions.’

It sounds miraculous. But how does this new release of Callas’s extraordinary recorded output differ from previous re-releases? Her recordings have already been remastered twice – once in the mid-1980s, when they were transferred to CD, and then again in 1997 to mark the 20th anniversary of Callas’s death – and there have also been other reissues in the Great Recordings series and elsewhere. What’s new? And why now?

Recording consultant Andrew Cornall describes himself as the ‘éminence grise’ behind the project, and he has final approval of the results before they are offered to the public. He offers two reasons – one practical, one artistic – for the impetus behind the remastering. ‘Some of the original tapes from the 1950s are becoming increasingly difficult to work with, so it’s vital that we transfer them, using the most sophisticated technology we have, while we still can,’ he says. ‘And on an artistic level, we also now have the ability to show these recordings off in the best possible way. I haven’t always been a great Callas fan, but I realise that part of the problem was simply that the quality of the transfers had not been ideal. With the recent strides in digital editing, we knew we had the means to do a better job. These are some of the most extraordinary recordings ever made – take the Trovatore from La Scala, with Karajan conducting, or the mono Tosca with Gobbi and Di Stefano – and now you can hear them in pristine fashion, with the voices really shining out.’

Maria Callas – The Complete Studio RecordingsThe story behind the remastering process.

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Cornall is the ‘extra pair of ears’ who comments on work submitted to him by a team of four remastering engineers – Allan Ramsay (team leader), Ian Jones, Simon Gibson and Andrew Walter – based at Abbey Road Studios in London. The location has a strong connection with Callas’s output, for although she didn’t much like recording there (she preferred the now demolished Kingsway Hall) it is where all the disc-cutting took place.

Ramsay describes his aim for the project: ‘The best way to explain a high-definition remastering is to use the metaphor of a digital camera,’ he says. ‘Imagine the difference in image clarity between a 1-megapixel camera and a 12-megapixel camera. It gives an idea of the resolution we’re now able to achieve. A cymbal crash, for instance, creates frequencies that are audible to the human ear, but it also creates supersonic harmonics, which are not. Those harmonics can still be experienced as a vibration in the air, even if you can’t hear them. Until now it has not been possible to reproduce those frequencies for the public, as the possible range on a CD [which operates at 44.1 kHz and 16 bits] is too low. With high-definition, which can operate at 96 kHz and 24 bits, we’re extending the range higher, and with more detail, than ever before. You’ll experience that supersonic cymbal-crash almost as if you had been in the recording studio when it was made.’

The term ‘bits’ refers to the bit depth or resolution of the digital information The term ‘kHz’, stands for ‘kilohertz’ and refers to the frequency – or pitch – of a note. As a guide, the range of a grand piano is 28 Hz to 4.1 kHz, and humans can hear up to 20 kHz. A digital recording medium needs a sample rate which is double the highest frequency required, which is why, when compact discs were first produced in the early 1980s, it was thought sufficient for them to have a sample rate of 44.1 kHz, at roughly double the human range of hearing. A 96 kHz high-definition recording can obviously capture higher supersonic frequencies.)

There are several stages in the remastering process. The first task Ramsay faces is to research the background to the recording, and meticulously go through its original production notes. This is to ensure that the correct recorded material is being used, and to understand it in as much detail as possible. The starting point is the large filing cabinet of matrix cards in a corridor at the studios. (A ‘matrix’ is a metal disc used for the mass-production of LPs at the factory. The word originally derives from the Latin for ‘pregnant animal’ or ‘womb’. If you’ll allow a digression, it’s interesting to note that the production of LPs, which began in the early 1950s, employs terminology which reflects the gender stereotypes of the earlier 78rpm era when matrices included ‘mothers’ as well as ‘positives’ and ‘stampers’. There’s a ‘master’ tape, which is used to create a ‘matrix’, which in turn produces LPs.)

In the process of making an LP, a metal matrix is first created from a fully edited tape. The master tape is played ‘live’ while a recording turntable with a stylus cuts a lacquer disc from it. This lacquer disc is then electroplated at the record factory to produce a metal negative (the matrix.) From the time EMI produced its first 78s, every matrix has had a card assigned to it which states when the matrix was cut, and if any subsequent matrices were made. Sometimes a matrix would get damaged at the factory, or a revision would require a new one, or it would wear out. If a revision was made, a contemporary remastering engineer might look at why it was necessary, and incorporate such changes himself.

The matrix number – which in the case of Callas’s stereo La Scala recordings begins with the prefix YBX – is stamped onto the central blank part of the LP called the ‘lead-out’.

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The number on side 3 of Ramsay’s LP pressing of La Gioconda indicates that it was cut six times before it was released. ‘The matrix cards confirm there were issues with surface noise and processing faults. In these cases a new lacquer would be cut at the studio and sent to the factory to be reprocessed.’

In 1959 Abbey Road decided also to create ‘job files’ for each project, and subsequent matrix cards carry cross-references to these (stored in a nearby filing cabinet.) The job file contains much more detailed notes about the recording sessions, memos about the venue, and if any problems were encountered such as unwanted noise. They often also contain instructions from the producer. This is from the job file for the stereo Norma, for example: ‘Pages 166–167 in the score. Heavy traffic noise. Please use rumble filter, or if necessary bass cut higher up to eliminate as much as possible.’ These are instructions to the engineer responsible for cutting the lacquer from the master tape. The tape would be equalised at that stage to adjust the bass or treble as the producer saw fit, and any noise filters applied.

These instructions are invaluable to a remastering engineer, who, with the benefit of digital RetouchTM technology, will be able to solve noise problems in a way the original technicians could never have imagined.

In the stereo recording of Norma, the job files also reveal that a noise occurred during the introduction to the second verse of ‘Casta Diva’. ‘Please copy identical passage, p.183, and insert’ is the producer’s instruction. The original editor would literally have made a copy of the earlier bar, chopped up the original tape, removed the noisy part, and spliced the copied section in. ‘But in the days of analogue recording, when you copied a tape there would unfortunately be an increase in tape hiss, so for one bar the hiss suddenly jumps up in level,’ says Ramsay. ‘Fortunately they kept the offending piece of tape, and stuck it on at the end of the reel. We’ve digitised it, taken out the unwanted noise, and put it back in the aria. We’ve fixed it just as the original recording personnel and artists would have wanted, had they had the technology.’

Some instructions may be ignored. It is an unfortunate aspect of LP technology that as the stylus gets closer to the inner groove, the sound is worsened by ‘inner groove distortion’. Engineers would sometimes add high frequencies at the end of a disc – a process called ‘radius compensation’ – to correct this (a procedure that is now, of course, redundant).

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It’s also worth noting that the louder recorded music is, the wider the resulting grooves will be on an LP: the groove shows the actual sound wave. So in order to fit certain material onto the 25-minute side of a disc, producers faced tough decisions. They might reduce certain bass frequencies to make the grooves smaller, for example. These alterations (now superfluous) are all noted in the job files, and give Ramsay and his colleagues vital information for a comparison of the original LP release with the master tape.

Having read the matrix card and job file, the time then comes to find the original tapes, stored in tin boxes at the EMI archive in Hayes, Middlesex. These are brought to Abbey Road to be repaired, if necessary, and then digitised.

Various problems can occur to magnetic tape. Sometimes the glue from the editing process will come loose and accidentally stick parts of the tape to each other, or the joins might break apart during rewinding. Another difficulty is ‘sticky-shed syndrome’ caused by the deterioration of the binder (a glue along the entire length of the tape which holds the magnetic, recordable part of the material onto the plastic strip). Only a baking of the tape can help in this case. Fortunately the latter has not affected any of Callas’s masters, although many edits have had to be repaired.

Sometimes the edits are extremely plentiful. When Ramsay plays the final scene of Manon Lescaut from the master tape, there are little white strips of splicing tape every few seconds. Each time the tape is rewound they can come a little looser. Sometimes they break altogether, and then it is Ramsay’s job to repair them.

Callas didn’t only record on tape for LP; she recorded on wax for her earliest 78s on Cetra, and these wax discs were used to create shellac 78s. These recordings were originally leased to EMI for release on the Parlophone label in the UK, and are also being remastered as part of this project. Engineer Andy Walter is working on this in another part of the Abbey Road complex.

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First he tries to find the right kind of stylus for the disc. ‘There are rules about which stylus is appropriate for which year – 2.7 thousandths of an inch, or 4.0 thousandths of an inch, say – but in practice you just try them all until you find the one which works best, the one which will get as much information off the disc as possible,’ he explains. The sound is then digitised for RetouchTM editing, but because shellac is such an inherently noisy medium, it is run through a two-stage automatic ‘declicking’ programmes – one for larger clicks, one for smaller – which can remove about 25,000 clicks per second. (The declicking programme is made by a company called CEDARTM, which also developed RetouchTM.) There’s also a programme to reduce surface noise and hiss. ‘It’s always a juggling act about what you take out and leave in. Some people think that the noise is authentically inherent to the 78 medium – that’s simply what shellac should sound like. I feel that as long as we don’t alter the voice, we’re doing a good service.’

Allan Ramsay agrees, and stresses that the remastering process should not interfere artistically with the original recordings. ‘We just want to present the recording as it was meant to be heard – as they heard it in the control room, and just as it was approved. We’re simply correcting faults just as the original producers would have done, had they had the technology.’

Walter plays a 78 of ‘Casta Diva’, and then switches between the original copy and the declicked version. It’s like a veil being drawn aside. ‘When the clicks and noise disappear, it’s as if the singer is suddenly standing much more clearly in front of you,’ he says. ‘And this is actually a beautifully recorded 78. She’s right there in front of the microphone, blasting away, but it sounds great.’

While Andrew Walter is dealing with the 78s (and chasing collectors, trying to track down a version of the ‘Liebestod’ which was never released in the UK), Ramsay is working on the tapes. Firstly he prepares the tape machines for correct playback. The remastering engineers select an EMI Calibration tape dating from the period of the particular recording and containing a series of tones in the form of long beeps. This tape is played and the frequency response of the tape machine is adjusted accordingly.

Pitch is another matter of concern. ‘Tape speeds weren’t computer-controlled then, and were slightly at the mercy of the frequency of the mains electricity and the tape transport’, says Ramsay. ‘In fact, many LPs from the era were sharp, simply because the tape machines were running a bit fast when the

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lacquer was cut. And sometimes two tape machines would run simultaneously at different speeds during a session. If both tapes were used for editing, the pitch would jump between edits. Again, it was just the best they could do at the time. Now we can try to fix those problems.’

The tape recording is then played through an analogue-to-digital converter, which makes the sound available for digital editing. When the tapes were first digitised in the 1980s for CD release, the information was stored on video tape, and these tapes were used as the basis for the 1997 remastering. Now Ramsay and his team are returning to the original analogue masters for all their work.

The next stage is to open the digital files on the computer workstation and begin the process of editing and retouching. RetouchTM is a programme that creates a visual realisation of the recording by splitting it into multicoloured sound waves which travel horizontally across the computer screen. (Imagine an ultra-sophisticated electrocardiogram, and you’ll get a rough idea of what it looks like.) Any unwanted sound, such as the distant beeping of a car horn or traffic noise, can be visually isolated and removed without affecting the music.

People have sometimes criticised Callas’s voice for its wobble: her producer Walter Legge humorously suggested that it could even induce seasickness. It’s fascinating to note that part (but not all) of the problem was simply due the inadequacy of the recording equipment of the time. Her voice was so powerful that microphones and tape were occasionally unable to cope with it, and the result was an electrical ‘bubbling’ or ‘popping’ between the harmonics of her voice. The bubbling occurs, amongst other occasions, during the fortissimo climax of ‘In questa reggia’ in her 1957 recording of Turandot, conducted by Serafin. The bubbles, which appear as little black lines between the separated harmonics on screen, are not an accurate representation of her sound, so Ramsay carefully removes them with RetouchTM and restores Callas’s voice to how it originally sounded at the recording venue (in this case, La Scala.)

Once digitally uploaded and converted into RetouchTM visualisations, the masters are ready for cleaning up. In Tosca, a high descending squeal from a malfunctioning amplifier at the recording session is present. (It looks like a thin sloping black line on the computer screen, and is easily erased.) ‘Prior to RetouchTM the only way to try to fix this kind of fault would be to cut all the high frequencies – changing the whole sound,’ says Ramsay.

On some LPs, made in Kingsway Hall (where Callas recorded Il barbiere di Siviglia, the second Lucia

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di Lammermoor, and the disc of ‘Mad Scenes’) London Underground Central Line tube trains can be heard rumbling away below the venue. The rising buzz of an accelerating Vespa is heard from the streets outside La Scala during the stereo Norma too: it looks like a rising black line on screen. All these sounds can now be removed, with a few simple clicks of the pointer and without affecting the music.

Sometimes an original edit isn’t quite correct. If a little too much tape was left in (creating a ‘double attack’ on the note), it can be corrected by removal. If a little too much was cut out, the problem is magnified. ‘If a tiny snippet is missing and there’s a rush in tempo, all the tools in the world may not be able to fix it,’ says Ramsay.

On recital discs, a problem can occur between tracks. The original editors inserted strips of plastic leader tape (blank white tape) in the spool between arias, so that there would be rills (wide separating bands) on the LP when it was cut. ‘On an LP such as Maria Callas Sings Rossini and Donizetti Arias, the surface noise of the vinyl masks the sudden silence,’ says Ramsay. ‘But when you play the original tape, or hear it digitally, it really jars. So we have to find some atmosphere – the sound of the empty room – from the Salle Wagram in Paris where she recorded it to insert at those points.’ (When the exact atmosphere from the original session is unavailable, Ramsay will search for a close match from a library collection of ambience sounds.)

‘Magnetic print-through’ is another hazard. Sometimes when the music is very loud, it ‘prints through’ to the adjoining piece of tape during storage on the spool. ‘The audio is recorded as a magnetic field. The louder the music, the stronger the field,’ says Ramsay. ‘It can affect the next layer of tape, and sound like a pre-echo, or post-echo, depending how the tape was stored.’ There is an echo of this sort during an orchestral climax in Il trovatore: it becomes visible on screen and can be straightforwardly rectified with RetouchTM.

Once the audio is fully cleaned up, it is passed – where necessary – through an equalising (EQ) desk to adjust the bass or brightness or add other effects required by the producer just as it would have been in the 1950s. There is a software programme which digitally recreates the effects of a manual mixing desk with all its faders and dials, but Ramsay prefers the old, non-virtual analogue version. ‘There’s a warmth to the sound with analogue EQ which we like, but we’ll use digital if it’s more appropriate. We’re lucky to have the option.’

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The recording is then tracked, or ‘PQ-ed’. Ramsay explains: ‘A CD can contain various sub-channels of information as well the audio. These sub-channels are named P, Q, R, S, T and so on, up to W. The P and Q channels are used to store, amongst other things, the track start & timing information.’ Even this process has been overhauled. Some of the CDs from the 1980s, the mono Tosca among them, were assigned only two tracks, and this would now be considered too few. More PQ tracks have been added, and the PQ plot of each opera has been rationalised across the entire project. For example the plot is now the same in both the mono and stereo versions of Tosca, Lucia, Gioconda and Norma.

For CD, the digital files are then processed by a sample-rate converter and dither, which reduces the output to 44.1 kHz and 16 bits. These files are sent to the CD factory, so that a glass master (the CD equivalent of an LP’s metal matrix) can be made. For the downloadable high-definition release, the files are left alone and remain at 96kHz/24 bit.

Is Ramsay ever worried about overstepping the mark? Is he concerned that some of the technical ‘clean-up’ alterations might be considered as a form of the artistic interference he is so keen to avoid? ‘If we ever have a doubt about something, we leave it alone. And if we’ve remastered something well, nobody should be able to notice it. We’re simply removing the inefficiencies of the recording process of the time. All we want to do is remove the specks of dust, as it were, and wipe the glass clean. We’re presenting the recording in the best possible light, and as the artists would have wanted it to be heard.’

© Warwick Thompson, 2014