The EMT 251 Digital Reverberation System, expands and surpasses the capabilities of its predecessor, the EMT 250 Electronic Reverberator Unit, in every respect. The total storage time of the EMT 251 has been increased so that in addition to pure reverberation a number of discrete reflections with a combined time of up to 120 ms are possible; the time and amplitude of three of these may be individually adjusted and are assigned to the left output, to the right, and to both through a panorama potentiometer.
The fourth delay function of the system triggers the onset of reverberation and is accompanied by six adjustable elements that govern a set of individual reflections. These reflections are arranged in a specific pattern and facilitate a smooth transition from distinct reflections to the start of reverberation in a suitable manner. The amplitude fader linked with this function dictates the correlation between the initial direct sound and the ensuing reverberant sound, thus establishing the size of the reverberation field. This feature empowers recording engineers to regulate a critical parameter that was previously beyond their command but holds significant value in the recording process.
Circuitry
To meet conventional studio demands, the EMT 251 Digital Reverberation System utilizes a balanced audio input. The input signal is digitized by a 16-bit converter and then processed through a hybrid processor. This processor generates the required data for both the reverberation effect and the individual reflections.
The analog signal is then reconstructed at the processor’s output and typically directed to two output amplifiers. However, the system can be configured with four outputs upon request.
Improvements in Technical Data
The system has an extended frequency response of up to 14.8 kHz, allowing for individual adjustment of the reverberation times at low, medium, and high frequencies. The analog-to-digital converter and its inverse now possess a word length of 16 bits, leading to a notable decrease in modulation noise. The enhanced audio bandwidth is especially beneficial in cases where the unit is utilized for signal delay purposes.
Indicators
An additional new feature on the EMT 251 is the comprehensive visual indication of all selected parameters using a liquid crystal display. The frequency spectrum of the reverberation time as well as the amplitude-to-time distribution of the first reflections are depicted in two overlapping curves. Thus the user can inform himself of the selected values at a glance.
Remote Control
All parameters of the EMT 251 may be varied by remote control using DC voltages. In addition, all selected values can be entered through a DC interface (e.g., HARRISON) into a computer or recorded simultaneously by an audio tape machine together with the values for the channel level controls. The EMT 251 Digital Reverberation System can then be controlled directly by the computer or from magnetic tape during mixdown.
The same remote control connections may also be used in conjunction with a bank of potentiometers adjusted to certain, frequently recurring settings, which may then be conveniently selected whenever required.
Reverberation
This program is used for generating extremely natural reverberation with variable reverberation decay times of 0.4 to 4.5 seconds. In addition, the relationship of reverberation time to frequency can be varied to a wide extent, expressed in each frequency range as a corresponding factor of the basic reverberation time:
- for bass frequencies (300 Hz) – factor of 0.5 to 2
- for mid-range frequencies (4 kHz) – factor of 0.2 to 0.85
- for treble frequencies (8 kHz) – factor of O to 0.85
Three discrete first reflections can also be adjusted: one is permanently assigned to the left output channel, the second to the right, and the third variably to both through a panorama potentiometer. The delay time for each reflection can be set between O and 80 or 40 and 120 milliseconds and the level between O and 100 %. Immediately at the commencement of natural reverberation (the time of which is set in the unit with a fourth control), a certain number of discrete reflections occurs.
This phenomenon is simulated by a cluster of six reflections fixed in their relationship to one another. The amplitude of this cluster is separately adjustable; if it be set to zero, the initiation of reverberation sounds soft and diffused, if set to 100 %, then direct and present. This adjustment thus permits the reverberation radius to be influenced.
Space I
This effect program exhibits a maximum reverberation time of 15 seconds. Its frequency distribution can be influenced by the treble control, thus changing the coloration. In other respects, its properties correspond to those of the Space Program in the predecessor model, the EMT 250.
Space II
With this program, the pitch of the perceived reverberant signal can be changed dramatically. The illusion is thus produced that the reverberation is moving about in space; the impression of distance is achieved by utilizing the Doppler effect.
Non-Lin
By establishing a non-linear reverberant delay-time characteristic, a substantial concentration of individual voices can be achieved without producing the impression of excessive reverberation. Two reverberation processes are superimposed to prevent substantial decay in a time of less than 0.5 seconds; that is, the original signal is first highly concentrated and then rapidly decaying.
Echo
The Echo program is implemented using loops, the lengths of which can be programmed and the feedback factors adjusted. A main loop is situated ahead of three auxiliary loops, permitting different adjustable effects in both channels.
Chorus
The Chorus program is employed to multiply voices or groups of instruments. The intensity of the effect as well as its variation speed can be separately controlled.
Delay
Up to nine individual delays (six of which, as in the case of reverberation, are grouped with a fixed relationship to one another) can be programmed with respect to time and amplitude.
Physical and Mechanical Arrangement
The EMT 251 Digital Reverberation System is designed to stand freely and features a power supply located in a bottom chassis to prevent interference with delicate circuitry from the AC power leads. The unit is partitioned with the analog section on one side and the digital section on the other, both accessible by tilting out the side panels for maintenance. The four panels of the system are made of black anodized extruded aluminum to ensure efficient heat-sinking for the power stages. The upper section of the unit houses the control electronics and operating panel.
2 Responses
I began my Goldust Recording Studio business in 1965. At that time we built an underground echo chamber with floor, non-parallel walls and ceiling made of reinforced poured concrete. This echo chamber served me well. In 1972 I purchased an EMT 140 ST which was moved to our new building in 1975. This unit became our primary reverb for the next several years and is still a great sounding unit. In May of 1990 after researching major studios and their equipment listings in Billboard Magazine’s industry sourcebook, I came to the conclusion that the studios which had an EMT 250 or EMT 251 digital reverb in their equipment lists were making great sounding records.
My curiosity led me to call the EMT distributor, Gotham Audio, in New York City to find out more about the EMT digital reverb. I was told the EMT 251 unit was being discontinued due to the arrival of less expensive units from Yamaha and others, but that the EMT 251 was an instrument in itself which was not being duplicated.
At that time, May 31, 1990, I was told Gotham audio had one demo unit in stock and one unit new in the box and were not expecting any more. They offered me a deal and I took it and never looked back. Now, with many great reverb plugins, I am still partial to the real EMT units.
Very cool story Emmit, thanks for sharing.