6-Series Limiters and Indicators
Sound Devices products are typically used for location recording of film, television, and broadcast audio.
This type of audio is often very challenging to capture due to the extreme dynamic range and unpredictability of program audio particularly in unscripted productions where dialog can go from a soft whisper to a loud scream without any warning.
To this end, a fundamental design feature of all Sound Devices products is to include high performance limiters at each gain stage, an expensive proposition, but one that is essential when designing a field mixer/recorder for wide dynamic range applications. This is in stark contrast to competitive units which do not have limiters at each gain stage, especially at the trim stage.
Figure 1 shows a simplified diagram of the 6-series gain structure. There are three gain stages (each represented with a triangle): trim, fader, output.
Since these stages can apply gain, they can overload. As such, at each of these stages, an independent limiter is available to prevent overload. Particularly unique is the trim stage (where most gain is applied), as all Sound Devices products have excellent trim limiters. Sound Devices users can be confident that no matter the environment, they will capture sound which will not overload any portion of the mixer/recorder.
The 6-series products conveniently have one tri-color channel LED showing a simple indication of a channel’s signal activity at a glance.
- The LED glows green in proportion to the trim level, such that even with the fader turned down, the user can observe activity on the LED.
- A peak overload (with limiters turned off) at either the trim or fader shows as red on the LED.
- Limiting at either the trim or fader shows as yellow on the LED.
NOTE: This LED is not a trim LED nor a fader LED, but rather a channel LED.
With default settings, the trim and fader both have the same limiting threshold – a few dB shy of clipping. This means that in all normal situations the limiters do not engage at all. This also means that it is easy to know which limiter (trim or fader) is limiting; if the fader is set above 0dB, the fader will limit before the trim stage. If below 0dB, the trim limits before the fader. With the fader set to 0dB, then the trim and fader stage start limiting at the same time.