Reel-to-reel master tapes have the ability to convey the ambience of a venue like no other recording medium. Hi-fi journalist Neville Roberts looks into some of the techniques used in modern recordings that can really help capture the atmosphere of the performance venue.
Making a modern recording is a bit more complex than simply switching on a recorder, though it doesn’t seem that long ago since an album could be made by just sticking a microphone in front of the performers and hitting the record button. It became evident, however, that far better results could be obtained by using several microphones positioned strategically within the band or orchestra and mixing the signals together. Then along came stereo, and microphone positioning and setup played an important role in the imaging and spaciousness of a recording.
The polar pattern of a microphone is a very important consideration. This is the term used to describe the directional sensitivity of a microphone, or its ability to pick up sounds from different directions.
The simplest pattern is the omnidirectional microphone, which picks up sounds equally from all directions. A figure-of-eight polar pattern picks up sounds from in front of and behind the microphone, but not from the sides. A cardioid pattern is, as the name implies, a heart-shaped polar pattern (actually an inverted heart-shape) where the microphone is most sensitive to sounds in front of it, less sensitive to sounds at the sides, and insensitive to sounds coming from the rear.
In the early days of recording, there were only omnidirectional and figure-of-eight microphones. Omnidirectional microphone diaphragms measure sound pressure at a single point in space, and because they have no directional information, they are equally sensitive to sound from all directions. Figure-of-eight microphones measure the difference in pressure between either side of an open diaphragm. This means that they are very sensitive to sound from the front and rear, but almost completely deaf on the sides. Then it was realised that by combining the signals of both omnidirectional and figure-of-eight microphones, you could achieve a cardioid polar pattern. The sensitivity of a cardioid is doubled at the front where the positive signals from an omnidirectional and figure-of-eight combine. The sensitivity remains the same on the sides as there is only the signal from the omnidirectional microphone; at the rear, the negative signal from the figure-of-eight element cancels out the positive signal from the omnidirectional element.
Further developments in microphone technology allowed for one microphone to have a polar pattern that was switchable between all three patterns. The Neumann U47, for example, can operate as either a cardioid and omnidirectional microphone, and the U48 can switch between cardioid and figure of eight patterns. Some types of microphone, such as the AKG C12, can offer a blend of these three patterns.
Location, location, location
Apart from the choice of microphones, the position of the microphones is very important. A crossed pair uses two directional mics that are crossed and this arrangement is often used to record solo instruments in stereo. The spaced pair configuration employs two omnidirectional mics spaced about 60cm apart. This is very good not only for recording the instruments, but also for capturing the ambience of the recording environment. The mono signals from each microphone are assigned to the left and right channels of a stereo track to create the stereo image.
The stereo image can be enhanced by the use of a Jecklin disk, which is a sound-absorbing disk placed between the two microphones to create an acoustic shadow from one microphone to the other. The technique was invented by Jürg Jecklin, the former chief sound engineer of Swiss Radio, in order to produce what he called an Optimal Stereo Signal (OSS). This 30-35cm disk is made from a sound-absorbing material, which acts as a baffle to help recreate the variations in frequency response, time, and amplitude that we experience when a recording is reproduced through loudspeakers.
A spaced pair of microphones, together with a Jecklin disk, is the approach used by Mike Valentine of Chasing The Dragon with all his live recordings. In a recording studio, multiple microphones can be used to record the performers, and while monitoring the rehearsal on loudspeakers in the mixing room, the recording engineer can make proper adjustments at the mixing desk to ensure that all the instruments are being captured correctly. However, there is nothing quite like a live recording at a remote venue. A live recording has the added benefit of being able to capture the acoustics of the environment as well as the music. However, this has its own challenges. At a remote venue, any mixing would have to be undertaken while listening on headphones, and if you get this wrong, a recording could be ruined. So, unless you are recording in a recording studio, it is far better to record a pure analogue stereo recording with a simple pair of correctly positioned microphones.
The distance between the microphone assembly and the performers is crucial for capturing not only all the detail from the instruments, but also the ambient acoustics from the venue. If you position the microphones too close to the performers, you risk accentuating instruments close to the microphones and losing detail from the instruments further away. Furthermore, much of the ambience of the recording venue will be lost. Conversely, positioning the microphones too far away from the performers and the subtleties of the instruments are likely to be swamped by the resonances and other noise from the venue. Getting the position exactly right is extremely difficult and relies heavily on the skill of the recording engineer. If you get it perfect, the listener can really be transported to the venue in his or her own listening room. A fine example of this is Chasing The Dragon’s latest tapes of recordings featuring the Locrian Ensemble playing, amongst others, Beethoven’s Fifth Symphony at St Martin in the Fields in London. This is the first of a series of tape recordings of Beethoven’s music. I am reliably informed that the next recording will be of Beethoven’s Ninth Symphony performed by the National Symphony Orchestra at the Snape Maltings Concert Hall in Suffolk on Saturday 12th October 2019.
Yarlung Records of California has worked with Sonorus Audio to develop a process called Sonorus Holographic Imaging, which is designed to create a three-dimensional sound field with a unique sense of realism. Several audio channels are combined in order to capture the ambience information in the final stereo mix of their copy-master tapes.
Sonorus Holographic Imaging can use up to eight channels of source material in order to recover the most detail from the original recording. These channels are then recombined into two channels. This process is real time and fully analogue and the resultant stereo signal is recorded on 15 ips analogue tape. If the original recording contains true ambient or surround information, the listener can be immersed in a sound field that extends to almost 360 degrees, even though it is only reproduced from two channels.
I have experienced this imaging process first hand with superb master tape recordings of choral music by Yarlung Records entitled ‘Nostos’ performed by the Cal State Fullerton University Singers. Yarlung used the AKG C-24 microphones and added two additional mid-hall Ted Ancona Schoeps M222 valve microphones, which Yarlung recording engineer Arian Jansen fed into the Sonorus Holographic Imaging processor to create a two-channel mix. A proprietary matrix incorporating phase, timing and EQ information from the four microphones was used to reproduce a three-dimensional listening experience from two speakers. The resulting stereo signal was recorded using a Sonorus ATR12 analogue tape recorder. The result is really quite staggering. One of the tracks of the tape, Ēriks Ešenvalds’ arrangement of ‘Amazing Grace’ is both moving and captivating, right from the opening solo voice of the soprano Vanessa Yearsley. Furthermore, I have the impression of sitting in the auditorium with the singers in the Valley Performing Arts Centre at Cal State University, Northridge, California, where the recording was made.
Another recording made by Yarlung in 2018 is a breath-taking Private Organ Recital performed by internationally-acclaimed organist Jung-A Lee in the Walt Disney Concert Hall. This recording was made with an AKG C-24 valve stereo microphone and two additional midhall Schoeps M222 valve omnidirectional mono microphones. These four channels were fed into their analogue Sonorus Holographic Imaging processor and the resulting two channel mix was directly recorded on their Sonorus ATR12 analogue tape recorder. Here again, the Sonorus Holographic Imaging does indeed convey an uncanny realism. The quality of the recording, the quality of the playing, and the quality of the compositions are all superb, ranging from the light-hearted ‘Hamburger Totentanz’ by Guy Bovet and ‘Miroir’ by Ad Wammes to the breath-taking ‘Ciacona in C Minor, BuxWV 159’ by Diderich Buxtehude and the famous ‘Prelude in B Minor, BWV 544’ by J. S. Bach. With this recording, I am transported to the Walt Disney Concert Hall for a fraction of the cost of the air fare!
Things have certainly come a long way from singing into a horn on a phonograph recorder!
Neville Roberts is a man of many interests and talents. As well as being a regular contributor to Hi-Fi Choice magazine, he’s a retired UK National Health Service (NHS) director, electronics engineer and physicist. He’s also a lifelong audio enthusiast with a particular interest in valve/tube audio design, and a devotee of vinyl and tape. Neville enjoys an eclectic range of music including classical, especially baroque, light orchestral and jazz. He lives with his wife near Bournemouth in Dorset, UK, where he grows orchids and is a keen photographer.