The EMT 970 Audio Delay Unit was a sophisticated and innovative device developed to address the challenges of manipulating sound transmission times in professional sound recording, reproduction, and broadcast technology. It enabled precise delays of audio-frequency signals ranging from 25 to 250 milliseconds, aligning these delays with the requirements of sound recording, studio acoustics, and aural-physiological processes. This made the EMT 970 a valuable tool for improving sound quality and achieving a variety of technical and creative audio applications.
The unit’s construction featured a stable frame design, housing a series of plug-in units. These included a stabilised power supply, mechanical components, and amplifier cards crafted from glass-epoxy materials for durability. The amplifiers exclusively used silicon planar transistors, ensuring reliability and high performance. At the core of the EMT 970 was its mechanical system, which relied on an advanced, durable Mylar foil tape stretched over a rotating drum-like surface.
This foil was coated on its underside and ran in an endless loop, with no splice gaps to disrupt signal consistency. The smooth, uncoated Mylar surface worked in tandem with magnetic recording heads, which were designed with mu-metal shielding to reduce interference and optimise performance. These heads were spring-mounted to maintain constant contact with the magnetic foil, ensuring minimal wear and maximum reliability.
The signal path within the EMT 970 was a hallmark of precision engineering. Incoming audio signals were fed through a record amplifier to the magnetic drum, where they were processed and then passed across three playback heads. Each head produced a distinct delay, and these signals were routed through individual equalised playback amplifiers. A user-selectable output bus allowed engineers to control the delay configuration with flexibility.
The system also supported mixed and separate outputs, which could be fed to other equipment or facilities as needed. In its stereo version, the EMT 970 incorporated two complete sets of amplifiers, further enhancing its versatility.
The EMT 970 was designed for a wide range of applications, making it indispensable in both creative and technical scenarios. One key application was in controlling room acoustics by delaying the first reflections of sound to preserve the transparency of large spaces. This allowed for a more accurate acoustic impression of a room while maintaining its characteristic reverberation properties.
In addition, the EMT 970 could create controlled echo effects, useful in music production and radio dramas. Delays of 125, 150, or 250 milliseconds enabled engineers to achieve natural or exponentially decaying echoes, enriching the overall sound experience. The EMT 970 could also be used to introduce a pre-delay to reverbs, including the EMT 140.
In technical environments, the EMT 970 excelled at addressing synchronisation issues. During satellite transmissions, for example, it compensated for discrepancies in the arrival times of audio and video signals, ensuring seamless broadcasts. In large venues such as concert halls or sports arenas, the unit’s ability to manipulate sound delay improved intelligibility and clarity.
By leveraging the Haas effect, the EMT 970 delayed secondary signals to match the primary source, reducing the confusion caused by multiple sound sources arriving at different times. It also played a critical role in foreign language dubbing and post-synchronisation of TV broadcasts, correcting lip-sync issues with precision.
The EMT 970 represented a significant technological achievement, offering a highly reliable and flexible solution for sound delay challenges in a variety of professional contexts. Its advanced design, robust construction, and wide range of applications ensured it became an invaluable tool in electro-acoustics, studio production, and broadcast technology.
This device opened up new possibilities for improving sound transmission and manipulation, firmly establishing its place as a pioneering product in audio engineering history.
