FM sound processing
Under FM Sound Processing (often short even sound processing , English for sound editing.) Is defined as a mid-1970s, initially in the US by Bob Orban developed methods for improving the modulation of FM - radio stations . With the advent of commercial radio stations in Germany in the mid-1980s, sound processing also found its way into the broadcasting scene here .
In sound processing, the level , dynamics and frequency spectrum of the audio signal are prepared in real time according to adjustable specifications , often in a single device over several processing stages. Modern fully digital sound processors usually include u. a. following or similar levels:
- AGC ( Automatic Gain Control ) for level adjustment of the input signal delivered by the studio
- Bass enhancer
- Equalizer
- Multi-band compressor / limiter for signal compression
- HF enhancer (addition of harmonics )
- Clipper (peak limiting) and
- Composite clipper (MPX limiting).
The de facto standard are devices from the US manufacturers Orban ( Optimod ) or Omnia ( Telos ). In addition, other devices such as stereo image processors Stereomaxx , Leveler or similar are sometimes added to the transmission signal chain (Airchain) . switched. Due to its high complexity, sound processing is usually set up by specialized experts .
In practice, however, it often turns out that due to this high level of complexity (and the differences in the music material being played), non-linear distortions ( overdriving of the modulation) and compression artifacts occur due to processing that is not optimally set (which can be seen in the loud "pumping" volume). Quiet music passages are raised too much in level, whereas loud passages sound "squashed".
In the meantime, there are also requirements for volume in Germany: With FM, in addition to the hub (<= 75 kHz), attention must also be paid to the MPX performance (signal density <0). The EBU R128 (-18 LUFS) was introduced at Digital Radio, so that broadcasters can move away from compression and back to dynamic, natural sound in order to make optimal use of digital technology without noise. It has been shown, however, that most broadcasters retain their original, unnatural and compressed sound and only lower their signal level so as not to exceed the maximum MPX performance. As a result, they are a little quieter and do not violate any support, but sound just as compressed as before.
There is already processing software such as B. RADIO OPTIMIZER, Breakaway, or Stereo Tool, which is also used in FM stations, because it delivers the same results as the expensive standard devices, but is more cost-effective.