Classical Recording

A Practical Guide in the Decca Tradition

Caroline Haigh, John Dunkerley, Mark Rogers

• Publisher: Focal Press
• Year: 2020
• ISBN:
  9781000194845
• Edition: 1
• Topic: Media & Performing Arts
• Subtopic: Music Theory & Appreciation

Classical Recording: A Practical Guide in the Decca Tradition is the authoritative guide to all aspects of recording acoustic classical music. Offering detailed descriptions, diagrams, and photographs of fundamental recording techniques such as the Decca tree, this book offers a comprehensive overview of the essential skills involved in successfully producing a classical recording. Written by engineers with years of experience working for Decca and Abbey Road Studios and as freelancers, Classical Recording equips the student, the interested amateur, and the practising professional with the required knowledge and confidence to tackle everything from solo piano to opera.

Part I

Before recording

Chapter 1

Acoustics and the recording venue

Capturing the musicians’ performance in a suitable acoustic space is central to the art of recording classical music. A good sounding space will enhance both the recording and the performance itself; playing music in a rewarding acoustic is a much more enjoyable experience than playing in a deadened room or a space with distinctive echoes or other problems. Reverberation from the room enables the players to hear their own playing better and thus helps with tuning and other performance attributes. Commercial record companies will spend a lot of time searching for halls and churches with a suitable acoustic characteristic, and as a result, many venues are used by multiple companies and freelancers for making recordings. However, it is not always possible to pick and choose the venue in a non-commercial situation, and so we need to consider what can be done in a less than ideal environment. The use of additional artificial reverb is an essential skill in classical recording, and this will be considered in Chapter 17.

1.1 Brief introduction to room acoustics

This book is intended to have a practical approach, and so for detailed discussion of theoretical acoustics and mathematical modelling of spaces, you should seek out an acoustics textbook. However, there are a few basic concepts that are worth including here.

Reverberation is built up from the repeated reflections of sound waves within a building, and after the very early reflections, it quickly becomes a blend of thousands of reflections and interactions that are no longer individually discernible. At every reflection of a soundwave, some energy will be absorbed and some will be reflected. This behaviour varies with the surface involved, and most importantly, it is frequency dependent. In a room where most of the sound energy is reflected at each interaction with a boundary, the sound will continue bouncing around the room for a longer time and produce a longer reverberation time. In a room where most of the sound energy is absorbed at each boundary interaction, the reverb will die down very quickly. After the first early reflections in the room, the reflections quickly multiply to form a characteristic reverb signature which is determined by a number of factors (see sections 1.1.1–1.1.4).

1.1.1 The materials making up the surfaces in the space

Any very smooth, hard surface will reflect more high frequencies (HF) than a rougher surface, which tends to scatter reflections and dissipate energy. Stone and glass will generate the most HF reflections, followed by painted, modern plastered walls and wood with a hard modern varnish. The more HF reflections there are, the more HF content will be in the reverb, and the space will have a bright reverb characteristic. Rougher surfaces such as oiled and waxed wood finishes will reflect less HF energy at each reflection, and carpets, curtains and upholstered seating will absorb higher frequencies very quickly.

Low frequency (LF) energy is absorbed very little by soft furnishings, but is taken up by structures with low resonances such as sprung floors and partition walls that are not solid. A lot of the energy from the LF waves will be taken up by these structures, making them move slightly, and will then not be reflected to form part of the reverb. A room with a sprung floor or partitioned walls can tend to sound bass-light when compared with one that has a solid floor and walls. An interesting example of a sprung floor was Brangwyn Hall in Swansea that had a floor with adjustable springiness so that it could be used as a dance hall. When Decca recorded there, the floor was adjusted to its firmest point to minimise LF loss.

Kingsway Hall (which was situated at 75 Kingsway, London WC2) was another very well-used recording venue. It had a sprung floor with a large void underneath that affected the sound in a different way. The void was used to store large rolls of theatrical fabric which were very absorbent, and they reduced the sound of the underground trains that ran beneath. This became apparent when the void was cleared out in the 1980s and the train sounds became more intrusive and amplified by the resonance of the now empty space. The floor and void in combination had a resonance in the 600 Hz region that actually enhanced the viola section.

Figure 1.1a and 1.1b show images from Kingsway Hall.

1.1.2 The size of the space

The larger the distance from the performers to the first boundary (a wall, ceiling, or floor), the longer the time taken for the first early reflections to arrive back to the players and any microphone placed near them. This timing gives a characteristic signature to the sound that enables us to judge the size of the space. A large space will also tend to have a longer reverb time because of the distances involved between reflections. A bathroom or a stairwell is likely to have a longer reverb time than a large softly furnished sitting room because of all the hard surfaces, but it will not sound like a large concert hall because the first reflections happen after a very short space of time. A useful rough guide is that sound takes about 3 milliseconds (ms) to travel 1 m (3′4″), or roughly 1 ms per foot. As noted in Chapter 17, artificial reverb is generally better at modelling the reverberation tail than the early reflections.

1.1.3 The geometry of the space

The geometry of the space includes both the shape and size of the room. Surfaces might be flat or curved, parallel or divergent, and these affect how sound waves behave in the room. Simple-shaped, small rooms with dimensions of around 3–10 m with parallel walls are susceptible to LF standing waves because the dimensions involved tie in with the wavelengths of frequencies in the 30–100 Hz regions. Parallel walls that are very reflective can produce a distinct series of echoes as the sound is bounced back and forth between them. These ‘flutter echoes’ are easy to perceive using a transient sound such as a hand clap to set them off, but they will be an unpleasant colouration on most sound sources placed between the walls. Rounded wall sections, as are sometimes found behind a church altar, can focus sound or can reflect it around the edges as in the whispering gallery at St Paul’s Cathedral in London. Temple Church in London has a rounded west end which produces some interesting focussing effects on the organ pedal notes, which are particularly noticeable just before the point where the rounded walls start. (See Chapter 14.)

Figure 1.1a A view of Kingsway Hall taken from the stage looking towards the balcony, which could be used for placing a chorus of up to 300 for recording. This image shows Anatole Fistoulari conducting the LPO with Mado Robin.

Photo: Courtesy Decca Music Group Ltd.

Domed ceiling areas can cause greater focussing of sound as they are curved in all directions, and it is usually a good idea to avoid setting the players up under a clearly defined domed area. Low ceilings will send very early reflections back to the players and will impart a rather boxed-in feeling to the recording, so any high ceiling would be preferred.

The effect of arched ceilings that are often found in older concert halls and churches is dependent on their materials; those that are made of a combination of ornate wood and plaster can work really well as they disperse the sound energy in a complex way that enhances the reverb time. Both Kingsway Hall (now demolished) and St Eustache Church, Montreal (used for many Decca Orchestre Symphonique de Montréal (OSM) recordings) have ornate arched ceilings. Where an arched ceiling is undecorated and made of hard stone, the effect is not nearly as pleasant.

Figure 1.1b A view of Kingsway Hall towards the stage with the balcony behind the camera. This image shows Sir Georg Solti conducting the LPO and Vladimir Ashkenazy playing the piano for Bartók sessions.¹

Photo: Courtesy Decca Music Group Ltd.

Figure 1.2 shows an image from St Eustache Church, with the seating removed and flooring in place for recording.

Figure 1.2 St Eustache Church and the Orchestre Symphonique de Montréal

Photo: Courtesy Decca Music Group Ltd.

Another interesting feature of churches are side chapels; if large enough, these areas can have their own distinctive reverb which only becomes audible when the players are playing loudly, and so their effect is unpredictable and intermittent. To locate the source of the problem you will have to go and walk around the church while the performers are playing.

1.1.4 The contents of the space

Soft furnishings, curtains, carpets, and padded audience chairs will absorb HF and mid frequency (MF) reflections and shorten the reverb time. The presence of an audience seated on hard chairs will shorten the reverb time in comparison with the unoccupied hard chairs (which is something to remember when moving from rehearsal to concert). Likewise, areas of wall surface that are uneven, such as areas of ornate wooden decoration or cases full of books, will disperse and absorb reflections and are very good for taming echoes. When running a recording session, two of the simplest things you can do to change the acoustics is to add or remove any upholstered audience chairs and open or close any large curtains.

1.2 What to be aware of when looking at a venue

When you first visit a venue that you are considering using (or having to use) for a recording, it would be useful to be able to get a feel for whether the space is going to produce difficulties or whether it is going to give you a usable reverb signature. Background noise levels must also be taken into account, and Chapter 2 contains further advice on visiting a potential venue.

Things to pay attention to immediately are:

• Traffic noise and aircraft noise. (Is there a quieter time of day? Can you record at night?)
• Buzzing lights. (Can you get them fixed? Work without them?)
• Air conditioning noise.
• Noises and cracking sounds from the heating system pipes (many venues have old heating systems that have to be run for quite a while before the temperature settles down and the noises stop).
• Broken panes of glass that might let birds in. Noisy birds within a church roof space are a common recording problem.
• Identify anywhere that that has some degree of acoustic isolation from the main space that you might be able to use as a control room.

In terms of assessing the acoustic suitability of the space, there are a few things you can do.

Firstly, visual clues:

• What’s on the floor? The surface most likely to produce good results for classical recording is a wooden floor over a solid foundation, with a natural finish such as spirit varnish, wax or oil. This will give some nice reflections and slightly more warmth as some of the HF is absorbed. A shiny polyurethane varnish or a stone floor will give a more brittle sound as it reflects more HF. Carpeted floor will absorb a lot of HF and MF and will be less enjoyable for the players if it covers the whole floor, although a small area of carpet around the performer can be a help if the floor reflections are very bright.
• Is it a sprung floor? If so, it could act as a bass trap and remove some of the LF reverb spectrum, depending on its exact properties.
• What’s on the walls and other surfaces? Stone will give brighter reflections, and too much HF can make the strings in particular rather tizzy and over-bright. Wooden areas are good, especially if they are rough or have a lot of architectural detail. This will disperse sound and mitigate against strong, distinctive single reflections. A minimalist glass and steel building with little in the way of architectural decoration inside will have a lot of distinctive HF reflections and very little to disperse sound energy, and as a result will probably sound coloured and horrible.
• Is there an arched ceiling? Again, if this contains a lot of wooden beaming, or panelling, it is likely to be beneficial, but if it is very unadorned stone, it will create a lot of HF reverb.
• Is there a dome? Are the players planning on sitting right underneath it? See if you can talk them out of this.
• Is the ceiling low? Be aware that a space that is too small in volume can become acoustically saturated quickly if the source is large and/or loud such as a brass band or orchestra. Playing something loud in too small a room is likely to be unpleasant for the players, and the recording will also suffer as the sound will not feel open with its full dynamic range but compressed and closed in.
• Are there any side chapels the size of small rooms that are enclosed on three sides? These will have their own reverb characteristics that might be triggered by loud sounds in the main space.

Then, some aural clues:

• Clapping at various locations within the building will give you an idea about the timing and quality of early reflections. Are there any distinctive echoes where the sound seems to slap straight back at you? Are there any areas of flutter echoes? You will also get a sense of what the HF decay sounds like, and whether the reverb is bright.
• Stand next to a wall and talk or sing at it – this will give you some useful information about what sort of frequencies the walls are reflecting. Hard plaster will reflect differently to older horsehair-type plaster.
• Making a variety of different frequency sounds around the building – hooting, squawking, and so forth; use your chest voice and head voice and see how the building responds to a variety of stimuli.
• To check for LF standing waves, you will need to be producing a substantial volume of lower-pitched sounds. See if you can set any off within the building. If you are recording something with organ, see if you can ask the organist to play some lower notes to check for any unusual acoustic behaviour.
• Stand at the position within the building where the performers are likely to be situated. Do sounds that are emitted here set off any unpleasant echoes, flutters, or standing waves? Do they activate any side chapel reverb if loud enough?
• Ask someone to walk down into the building and talk back to you from various places. They should do this without shouting or raising their voice so that the room is not excited to any great extent. The intelligibility of the speech will give you a helpful indication of the nature of the early reflections, and how...