With the arrival of the PC in every household, audio signals are more digital than ever. This also increases the lack of clarity of signal levels. This document explains how to deal with digital signals.
0 dB
The dB is a ratio, so a level of 0 dB does not say much, although some link 0 dB to an absolute level, this is in fact incorrect. 0 dB in a digital file usually means: the maximum level in that file, so when all volume bits in the file are at maximum. Recording up to 0 dB is possible, but it is strongly discouraged; after all, if there is a signal of +1 dB, for example, the recording is worthless, because this signal can no longer be coded (0 dB was the maximum after all). When recording on a digital medium, a limit of -12 dB is usually adhered to, then there is enough space to record peak levels. By the way, always use a compressor limiter for recordings directly on a digital medium, so that the space of 12 dB is really sufficient. When playing files, -6 dB is often used, most players such as VirtualDJ have the option to listen to the next song while playing a song and to set an auto gain level so that the music tracks are approximately get the same level.
It doesn’t sound equally loud!
Yes that is logical, the levels are now the same but the compression level of the various tracks is not. For example, if you play a voice and a piece of music at -6 dB, the music will sound much louder. You can choose several options to solve this:
- also compress the voice with eg Adobe Premiere or Blackmagic Resolve
- turn down the music by about 6 db
- real-time you can solve this by using a compressor and you could use frequency dependance
- real-time you can also run everything through a compressor and thus ensure that everything is about the same level
- a combination of the above methods
SMTS itself uses a combination of techniques; we use the auto-gain of Virtual DJ and we use compressors, a 32 band equalizer and active filtering for the amplifiers for amplification.