by Angelo Farina
This is my first VST project, developed employing a very nice high-level VST development tool, called Synthedit (www.synthedit.com).
This plugin emulates �Bass Management�, as usually performed inside home-theater receivers/amplifiers, including the +10dB boost of the LFE channel, as mandated by Dolby specifications (this gain boost can be switched on or off through a switch).
The following picture shows the internal processing network of the �Bass Management� plugin:
Here the user�s interface of the Bass management plugin is shown:
The Bass Management plugin is freeware, and it can be downloaded from here:
Just download the file named Bass Management.zip .
Finally, in the same directory I also made available the source code (a Synthedit project). This is its graphical appearance inside Synthedit:
The project is named Bass-management.se1, and it can be downloaded from my web site, too.
For the same reason, the Synthedit project only works under the registered version of Synthedit (the shareware-demo-unergistered version of it only works in stereo).
Question: why the input channel n. 4 is labelled LFE, and the output channel n.4 is labelled Sub? What�s the difference ???
It's fairly important that you understand that there are two different audio signals that make up the subwoofer output (labelled Sub, output channel n. 4). The LFE channel is the channel stored in the DVD that you can use for Low Frequency Effects such as Dinosaur footsteps.
The goal for this channel is to store very loud �effects�, which would not fit inside the dynamic range of �normal� channels. In fact, the Full Scale value of the LFE channel is specified to be 10 dB louder than the full scale limit of the other 5 channels.
So, the LFE channel is for storing LOUD sound, whilst �normal� sounds, even if containing very low frequencies, should be left in the proper 5 �main� channels, which are specified to be full-bandwidth, including very low frequencies.
Don�t forget that the LFE channel is then amplified by +10dB (3 times louder) on the playback side of a Dolby Digital Decoder. If you are mixing for music you may not really need to use the LFE channel.
On the other side, most surround systems employ 5 small satellite loudspeakers, which cannot reproduce low frequencies, and a powerful subwoofer box. The surround amplifier takes care of this, routing the low-frequency contents to the subwoofer, where they add up to the LFE signal. Of consequence, the SUB output of the �Bass Management� plugin contains the LFE (boosted by +10dB), but it also contain the low-end of the contents of the other 5 channels.
If the connected external subwoofer is already regulated for boosting the sound by +10 dB, then the �internal� boost of the plugin should be turned off.
Of course, if the LFE channel contains frequencies above the cutoff frequency of the subwoofer, this hi-frequency content is instead routed to the 5 main speakers�. This is NOT being boosted internally by +10dB, whatever the setting of the switch, for avoiding digital clipping on the outputs of the 5 main channels.