Video Registration audio Signal Processor
Custom design by Marc Marc for "Henk van Dijk Camera Works"

Photo of front panel

functional block diagram

____ The VSP counts the following modules & features:

  • 4x High Quality/High Gain Pre Amplifiers
    • Symmetrical MIC input
    • Asymmetrical Line input
    • MIC/LINE input switch
    • Phantom MIC on/off switch (48V)
    • LED indication Phantom on/off
    • Initial MIC gain select: 30,40,50,60 dB
    • MIC/LINE Second Gain Control
      -20....20 dB (total gain up to 80 dB)
  • 4x Compressor / Limiter
    • Response time select: Slow / Normal / Fast
    • Function select: Limiter / Limit & Compress / Compressor
    • Selection switch:
      (Normal / OFF / limit & compress)
    • Level indication LED (green)
    • Act LED (red) - Limit/Compress action
    • Overload indication LED (large red)
  • 4x High Cut filter (treble)
    • 4x Cut off control pot.
  • Mixer
    • 4x mono to stereo panning controls
    • 4x level (mix) controls
    • Stereo LED VU meter
    • Output volume and Balance control
    • Headphones output with gain control
    • 2x XLR and Cinch outputs
  • High quality power supply
    • Main filter
    • LED indication 'main Fuse OK'
Photo of rear panel

Viev full specifications & Explanantion: Dutch . . . English

Functional Description

A company for Television Video registration in the Amsterdam Opera/Concert Hall wants to have a compact device to be able to record the sound of the concerts with 4 microphones to have a high quality sound recording to later mix together with the video shooting. But, buying 4 high quality microphone preamplifiers with Phantom capabilities + 4 compressors / limiters/ + equalizing for 4 units and an end mixer + headphones and VU meter, is not only very expensive but also takes much transport/setup space and is a hassle to wire up every time (besides the increase of error due to this complicated setup).

Much better is to have a single box (19 inck rack) designed with all features nessecary without an overhead on features. All designed to exactely match the recording requirement. The result, in this particular case, was the VSP. A Video registration Sound Processor - based on professional technology to suit for professional productions.

I will explain the VSP by simply letting you follow the path of actions on scene which each time need to be taken for a registration.

First the Microphones are plugged into the VSP (up to 4) and put on the recording scene. Based on knowledge of the MIC type and the expected input signal, the initial gain is set by a switch - ranging 30 to 60 dB. Also, the Phantom switch need to be set ON for those MICs which require the Phantom Power line.

Then, when rehearsing, the secondary gain control is set (-20...+20 dB) to have the MIC's receive nominal levels. This means that the total gain of a MIC can be set anywhere between +10 and +80 dB (3x...10.000x amplification).

The next step is to decide whether Compression and/or Limiting is required for each channel. The VSP counts for each of the 4 channels a Compressor/Limiter. They are specially designed for microphone picked-up signals in a LIVE situation. With a MODE switch one can select the mode for Compression, Limit or a combination of both. Compression is selected when the MIC needs to pickup both little and loud sounds. The little sounds which you may hear good when your are LIVE hearing the concert often does not come true on a straight forward recording and the loudest parts are often to load to reproduce on television. Thus compressing this LIVE dynamic distance between the most little and the most loudest sound is required.
When also the danger exist that the source pickup by the MIC sometimes becomes extreme loud - and this only happens rarely or at very few occasions, then the Compression/Limit combined mode is valuable. This mode combines to compress the dynamics and at the same time puts a limit on the maximum level. All this to prevent distortion in the load parts.
When the minimum volume - picked up by the MIC - is not a problem because the dynamic volume change is of more concern to the high volume side, then the LIMITER Mode need to be used. This mode does not amplify the 'weak' parts extra (because they are considered to be on a propionate level for reproduction). The danger lies in the attenuated parts which for the LIVE ear might seem to be acceptable but for the recording and/or reproduction media over the limit (live dynamics easily are 120 dB while recording for Television broadcasting limitation to 60...70 dB is required to reproduce the registration in the setting of broadcasting. The VSP also features to BYPASS the Compressor/Limiter when not required at all.
Important is to be indicated on the levels. This because you like to know not only by the headphone monitoring how the levels are but also based on a more objective parameter. This is achieved with 3 LED indicators. A green 'glowing' LED shows you the strength of the incoming signal after amplification. A Orange (red) LED indicates the Compression/Limiting action that is taken by the VSP (even when you have it bypassed) and an OVERLOAD indication - Large and very bright LED - shows you on a large distance that you are into distortion and thus need to lower the gain.

After this, each channel passes through a high cut filter to get rid of unwanted high frequency spectral noise. How much suppression of the 'white' noise one would like to have depends also on the spectrum range of the source. When listening with headphones one can hear more noise (in particular when much amplification is required) than when sitting at home listening to the TV. One or another depends very much on editing experience. At least, the High Cut filters let you 'pre-edit' the sound within the noise reducing aspect. The cut should be always a little less than the subjective feeling appears into the headphones and are seen into the total sound landscape - which often is masking noise from a single channel.
This noise 'problem' only occurs when the sound source is too far away and/or bad MICs are used. The normalized Signal to Noise ratio (S/N) of the VSP is better than 80 dB (up to 90) with a general amplification of 60 dB.

At this stage the most important tasks are done. Now it is only a matter to mix the 4 channels to a stereo mix. The VSP has a high quality mixing and balancing stage to bring out a stereo mix of the 4 channels.

After mixing a master volume and master balancing stage is followed. This end signal is brought out to the XLR outputs.
A headphones monitor is of course available, including a Phones gain control.
At last, the end mic LED VU meter lets you view the correct levels of the end mix.

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