EMT 252 Digital Reverb

It's no secret that the "EMT sound" is a key ingredient of many hit records. It's been that way for over 25 years. The very first unit, the EMT 140, is still used by major studios.

EMT 252

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And the sound of their big digital units. the 250 and 251, is legendary. Now EMT introduces their new concept of digital reverb - the EMT 252. It offers more programs and features than the 250 and 251.

Details

Here’s what we mean:

  • Functionally clear, easy to operate control panel.
  • Non volatile storage for 128 groups of parameter settings.
  • Noiseless recall and sequencing of settings during audio programs.
  • 40nS digital processor speed coupled with 16 bit A/D converters yields 15kHz bandwidth and full dynamic range.
  • The original EMT 252 reverb program for superb sound at short decay settings.
  • The EMT 252 linear reverb program for perfectly natural sound at longer decays.
  • Chorusing, delay, echo loops. doppler reverb, and non-linear reverb programs.

 

The affordable 252: The superb EMT sound will not surprise you…the price will!

The EMT 252 Digital System is the successor to he well-known EMT 251. On the basis of that unit, which provides with lever switches,
and LCD indication, a unit for 19″ rack mounting with remote control has been developed.

Newly included are the 1 28 storage locations of the remote control. Half of these are preprogrammed with fixed programs; the other half allow free programming by the user. A tool has thereby been provided that significantly simplifies the task of finding appropriate
settings quickly and repeatedly.

The fixed programs are oriented toward musical instruments and rooms. In the reverberation program, for instance, settings are provided for saxophones, stringed instruments, brass and woodwinds, solo vocalists, choirs, and background choirs, as well as for the acoustical characteristics of various-size rooms with different reverberation times.

Operation
On the main unit, only the power switch, level indicators, and two status indicators are located. After the panel section (printed with the block diagram) has been opened, the input and output levels may easily be adjusted at the front panel. Regular operation is controlled, however, entirety from the EMT 252 S Remote Control Unit. First, the program is selected. In addition to the main program for reverberation, six effect programs are provided, as follows:

  • Delay Program for delaying four signal paths, with time and amplitude control. The maximum delay time is 480ms.
  • Echo The repetition time and feedback factor of four echo loops may be programmed; three of the echo loops are connected in parallel behind the first loop. The longest loop duration is 440 ms.
  • Chorus Program for multiplying individual voices or instruments (orchestra effect).
  • Non Linear Program with nonlinear reverberation decay curve. The signal is held nearly constant for 200 ms (very long reverberation time); thereafter, it decays extremely rapidly (very short reverberation time). The program serves to concentrate individual voices or instruments without conveying the impression of excessive reverberation.
  • Doppler Reverb Effect reverberation with long reverberation times and linear frequency response of the reverberation time. Through use of the Doppler effect (frequency shifting), an impression is created of moving sound sources within the room.
  • Space Effect reverberation with long reverberation times and linear frequency response of the reverberation time.

 

The various parameters may be varied within a program by selecting the function with the appropriate button and changing the value with the parameter lever. The functions and value ranges for buttons I through IV are provided in the table on the program selection field.

These parameters are always indicated. For the reverberation program, the value shown is the reverberation time at 1 kHz (large display) in the range 0.4 s to 4.5 s with the multiplication factors for:

  • low frequencies (below 1 kHz) 0.5-2
  • midrange frequencies (1 kHz to 8 kHz) 0.2-0.9
  • high frequencies (8 kHzto 15 kHz) 0-0.9

 

In the middle section of the control field, the delay times and amplitudes of a number of discrete reflections may be set. (Refer to the block diagram of the REVERB program.) The amplitudes are indicated in percent (%), the times in milliseconds (ms). The
reverberation time may be varied in the reverberation program between 0 ms and 80 ms; however, 40 ms may also be added to all reflections (+40 ms button), so that the time range lies between 40 ms and 1 20 ms.

The selectable time range is indicated in the TIME SCALE field. The PAN reflection is distributed to the two output channels with a panorama control. The adjustment is performed in 11 steps between 5 left through 0 center to 5 right. The signal path designated as CLUSTER produces a group of six reflections in a fixed relationship to one another, three of which appear in succession at each output.

The initial delay set for the cluster is also the setting of the initial delay of the reverberation in the classical sense. Subjectively, however, the perceived initial delay depends on the relationship in time of the remaining reflections to the beginning of the reverberation.

The manifold possibilities for setting reflections allow – independent of the reverberation time -room characteristics to be simulated, such as room size, reverberation radius, distance from the sound source, strongly or weakly reflective bounding surfaces, speech intelligibility, and acoustically very asymmetrical rooms.

The fixed programs may be called up from the PROGRAM MEMORY and user settings stored. The memory is divided into the sections ‘FIX” (for the fixed programs) and “USER” (for the freely programmable storage positions).

For the effect programs, eight fixed programs and eight USER programs are available. For the reverberation program, 16 of each are provided. With the reverberation program, either Bank A or Bank B must be selected by pushing the selector button twice. Occupied memory positions are indicated by the “LOADED” LED.

The SET function is activated in the upper right-hand section of the control field. In the “Permanent Set” mode all parameter changes are executed immediately by the processor, while in the changes are “Immediate Set” shown on the display, but executed only when the “IMMEDIATE” button is pressed.

Particularly during the production of radio plays or films, it can be important to recall sequences of preprogrammed settings rapidly. This may be accomplished with the “PARAMETER” lever. By pressing down on the lever, the function “Recall Next Memory Position” is executed and a SET  pulse automatically generated.  Sequences may also be recalled in this manner by remote control, for which a foot switch may be connected.

The level indicator and several status LED’s are located on the upper left. The “0 dB” LED indicates the calibrated nominal level and is set to 6 dB below the overdriving point (‘REGISTER’ LED). The ‘REGISTER’ LED is also activated if the processor is overdriven.

The status LED’s have the following significance:

  • Memory Error An error has occurred in the dynamic RAM on the digital board, or a storage unit is defective. The error is suppressed by the automatic correction circuit and remains inaudible. A defective storage chip is indicated by a row of LED’s on the digital board and thus may easily be replaced.
  • Memory Overflow In the echo program, times may be set
    with loops switched in series that cannot be realized in the memory. The LED then indicates that the maximum storage time has been exceeded.
  • Transmission Error The error detection circuit has determined that an error has occurred on the transmission path between the remote control unit and the reverberation system.
  • Temperature Alarm If the temperature rises excessively
    inside the EMT 252, the LED blinks. A recording in progress need not be interrupted, since a sufficient safety margin exists to protect the circuitry. After the recording has been completed, however, the cause of the alarm should be investigated. Usually, either the air intake or exhaust is blocked, or one of the fans is defective.

 

Design & Construction
The EMT 252 Digital Reverberation System employs (as does the EMT 251) an extremely fast signal processor with bit-slice circuits. By means of “pipelining” and parallel processing, extremely rapid processing times are achieved, so that an audio bandwidth of 15 kHz with high-quality reverberation can be attained.

The unit is provided with one input and two outputs that are balanced, exhibit conventional studio impedances, and allow matching to a wide range of mixing console levels.

The audio range is limited by high- quality 11-pole Cauer filters with delay time compensation, insuring that no aliasing effects will be heard. The audio signals are converted by 16-bit converters that afford a high dynamic range. Further operations are performed in the processor, in part with a word length of 20 bits.

The dynamic RAM, in which the audio signals are temporarily stored, employs a high-performance error correction circuit that can eliminate I-bit errors and recognize 2-bit errors. The memory is organized to enable correction of all errors when a storage unit becomes inoperative. In addition, the position of the defective storage chip is indicated.

The unit is designed for easy servicing. The digital board is located horizontally under the top cover plate, while the analog board and the remote control interface have been inserted through the front panel. An extension board is included in the unit as standard equipment.

The power supply with all fuses and adjustment components is easily accessible from below.

The remote control unit is connected through a two-conductor balanced line. The information is coded in 10-kHz tones. This interface point has been developed by EMT especially for studio data transmission and has already been employed (for the first time) in the EMT 245 S Remote Control Unit. The advantages of this transmission technique lie in the low signal level of approx. — 20 dB and in the signal spectrum itself, which rolls off at approx. 12 dB/octave above 10 kHz, thereby preventing the crosstalk problems of digital signals with absolute certainty.

The signal contains no DC component and may be transmitted via patch fields like normal modulation. Distances of over 100 meters may be spanned. The remote control unit contains a microprocessor which interprets the button signals, drives the displays, and implements communication with the main unit.

Transmissions proceed in two directions: the level information and status are transmitted from the main unit to the remote control, while program selection and parameter values are sent
to the main unit.

The fixed programs and the USER programs are stored in a CMOS-RAM that is buffered with a lithium battery. The data are thus protected for approx. 10 years, allowing the remote control unit to be taken into another studio.

For distances up to 20 meters, the remote control unit is connected directly to the EMT 252 Digital Reverberation System using the cable provided with the unit. Power is supplied through the cable.

For greater distances, an external power supply must be connected ahead of the remote control unit. In addition, the remote control unit may be connected to an existing EMT 251 Digital Reverberation System. In this case, an interface and an external power supply are required.

Specifications

Released: 1985

Quantization: 16 Bit
Sampling Frequency: Unknown
Frequency Response: 15k Bandwidth
Dynamic Range: Unknown
THD: Unknown

EMT 252 Remote

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