At the Volksoper Vienna, Austrian sound engineer Andreas Hendler has refined the classic ORTF microphone technique, developing a three-microphone variant now known as the Hendler-ORTF. This approach builds upon the strengths of the traditional ORTF setup, which is considered the best stereo technique for spatial reproduction, adding subtle tonal depth to the stereo signal. The result is an enhanced evolution of a proven recording method that has gained recognition in professional audio practice.
Hendler has been a part of the Volksoper’s audio team since 1992 and is one of the leading sound engineers responsible for the theater’s professional recordings. For more than three decades, his practical experience and curiosity for acoustic detail have shaped the development of the Hendler-ORTF technique.
From French innovation to modern stereo
In the early 1960s, sound engineers at the Office de Radiodiffusion Télévision Française (ORTF) developed, through a series of practical experiments and listening comparisons, a stereo main microphone system using two cardioid microphones spaced 17 cm apart at a 110° angle. This setup balances interchannel level and time differences to produce a realistic and coherent stereo image that closely matches how we perceive sound in real life.
Known as equivalence or mixed stereophony, this technique ensured even spatial distribution of phantom sound sources, with an effective recording angle of approximately ±48°.
Birth of the Hendler-ORTF technique
In an interview with the NYC Daily Post, Andreas Hendler recalled the moment that inspired his modification:
“One day I was making a classical ORTF recording at the Volksoper. Martin Lukesch (Head of Sound and Multimedia) remarked, ‘Something is missing.’ When I listened back, I realized that the tonality of the sound was lacking, because in the standard ORTF setup, the microphones mainly capture sound arriving from the sides. This means that the central sound components reach the capsules at an angle rather than directly, which slightly alters their tonal balance. To address this, I began experimenting with adding a third microphone in the center alongside the standard ORTF pair. This method proved effective — and soon, my colleagues started calling it the ‘Hendler-ORTF’ whenever recordings were to be made.”
The adaption of Hendler-ORTF is not about improving a missing center in the regular ORTF, but rather a tonal enrichment — a tonal improvement — making the sound “more plausible,” as well-known Austrian audio engineer Dietz Tinhof phrased it.
In practice, the third microphone — which varies between an omnidirectional and a cardioid capsule depending on the room acoustics — is positioned a few centimeters behind the ORTF pair, at least two centimeters away.
Hendler explained that in poorly sounding rooms, he rather uses a cardioid; whereas in well-sounding rooms, he prefers an omnidirectional capsule. Sometimes he even employs both, working with a fourth audio channel.
This slight offset allows the center signal to blend naturally with the left and right channels, enriching the tonal balance without compromising localization accuracy. Depending on the recording environment, the central capsule may also be angled or tilted to optimize spatial integration.
Hendler emphasized the versatility and consistency of his setup across a wide range of musical contexts:
“The microphone can be used for any configuration, and that is its greatest advantage — a mic setup that quickly delivers excellent results, even in acoustically challenging rooms. Whether for chamber music, solo instruments, or large orchestral ensembles, the outstanding three-dimensionality of the sound combined with the reduction of the tonal weaknesses of the conventional ORTF is the greatest reward! Especially for choral recordings, it produces very good results, as the tonal weaknesses in voices are particularly noticeable and are effectively reduced by the center microphone.”
The Hendler-ORTF system has been successfully employed in a variety of contexts, from opera productions to orchestral concerts and even Dolby Surround recordings. It excels with wide ensembles or complex acoustic environments, where a stable center and enhanced depth are essential. The array can serve as a standalone main stereo system or be complemented by additional spot and ambient microphones for greater flexibility.
At the Volksoper, Schoeps STC 4 microphones with Colette cables are used for both standard ORTF and Hendler-ORTF recordings. Their precisely engineered capsule spacing and angles ensure a natural and coherent stereo image. The standard ORTF array employs two MK 4 capsules from the Colette series, while the additional Schoeps ORTF microphone features an integrated amplifier.
Key stereo techniques
In audio recording, several standard stereo microphone techniques are used to capture spatial information in distinct ways.
XY uses two cardioid microphones crossed at a single point, producing stereo primarily through level differences. It provides sharp localization, though it may convey less sense of depth compared with spaced techniques. XY is known for its high coherence and almost mono-like stability because the center is very prominent.
AB employs two spaced microphones and relies on time-of-arrival differences to create stereo width. Typically using omnidirectional microphones, this technique can produce an expansive image, but the sound field is not always natural and depends heavily on the recording environment. It works best in acoustically well-balanced rooms.
Blumlein, named after Alan Blumlein, is a stereo system using two figure-8 microphones crossed at a 90° angle. The stereo effect is created through level differences (intensity stereo) rather than time-of-arrival differences. It provides a natural sense of space and a wide stereo image and is suitable for any true pressure-gradient microphones, such as condenser or ribbon microphones.
The Decca Tree, widely used for orchestral recordings, depends strongly on room quality. It arranges three omnidirectional microphones in a “T” formation to capture depth and spaciousness. Its configuration emphasizes a balanced front-to-back perspective and a stable stereo image over a wide ensemble.
The Jecklin Disc, named after the Swiss sound engineer Jürg Jecklin, is a spaced-microphone system in which two omnidirectional microphones are positioned on either side of a 16.5 cm sound-absorbing disc. It produces a natural-sounding stereo signal, with directional information conveyed through both time-of-arrival and level differences, similar to the acoustic effects of the human head.
As mentioned before, the ORTF system, developed in the early 1960s, uses two cardioid microphones at a 17 cm distance and a 110° angle. By combining level and timing differences, ORTF balances spatial accuracy, tonal coherence and ensemble breadth, making it a widely used and reliable stereo technique.
The Hendler-ORTF, named after sound engineer Andreas Hendler, further refines this method by adding a third, central microphone — which may be either omnidirectional or cardioid depending on the room acoustics — behind the ORTF pair. This addition enriches the tonal depth of the stereo signal while preserving the natural balance of the ORTF system, offering an enhanced yet faithful evolution of a proven recording method.
Passing on a unique listening philosophy
Through his work and the development of the Hendler-ORTF, Andreas Hendler advocates for a recording philosophy rooted in attentive listening and practical experimentation. His method encourages engineers to combine technical precision with perceptual sensitivity, ensuring every instrument and tonal element is faithfully represented in the stereo field. The Hendler-ORTF thus stands as both a practical innovation and a statement of artistic integrity — preserving the authenticity of the acoustic experience.
Featured image: Photo by Martin Lukesch
Edited by James Sutton
