Audio 'normaliser'
Chris Roberts
On 17 August 2011 19:02, Edd Barrett <vex...@gmail.com> wrote:
> Audio electronics huh.
>
> Can you make a circuit to normalise audio signals coming from a computer.
> This is useful when you have many media files at varying overall "loudness".
>
> Wanted something that does this for some time.
>
Aha! Well, funny you should say that, I've been working on something
that does exactly that.
What you're talking about is *probably* an AGC (Average Gain Control)
or compressor. Unfortunately, 'loudness' isn't quite as simple as how
much voltage is going down the signal - the perception of loudness
depends on the content of the wave as well as the actual level.
Broadcasters use pretty complicated kit to make their output of
uniform 'loudness', and you will have probably noticed if you watch TV
the ads end up being louder than the normal programme. This isn't the
fault of the TV channel - it's because the ad agencies will compress
the hell out of their audio, giving it very little dynamic range and
make it sound louder (and usually crappier) - only when you start
doing very complex processing of the audio can you fix this.
To effectively limit the dynamic range of a programme as a whole, you
need to both AGC / compress the audio in the short term to prevent
peaks from increasing the dynamic range (and potentially distorting
the output) - but also control the gain over the long term (several
seconds) to 'turn up' or down the overall level.
I've written quite a long blog post about how to design such a device,
at least using blocks of several devices.
http://naxxfish.eu/2011/a-walk-through-a-broadcast-audio-processor/
So - you can make something that'll do what you want, but how well it
will do it will depend on either a) how much money you want to put
into it or b) how much time you want to spend making all the
individual bits that make it work.
Chris Roberts
~
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