[Ardour-Users] analog summing

Robin Gareus robin at gareus.org
Sun Dec 17 05:54:55 PST 2017

On 12/17/2017 01:17 PM, Matt Keys wrote:
> When is it appropriate, if ever, to use analog summation in the
> signal chain into Ardour? Is there a difference between analog
> summation using mixer output into the daw versus mixer output to a
> device like the dangerous labs 2-bus and then into the daw? I'm
> having difficulty understanding the whole 'more headroom' or 'more
> dimension' claims.

This particular device is from 1999. Back then those days it was common
to use fixed-point integer arithmetic for audio summing on PCs, usually
16 bit resolution ~= 96dB.

Not only does fixed-point clip when you exceed 0dBFS but with a large
amount of tracks it is no not very convenient to work with.

These days almost all DAWs use 32bit floating point for internal summing
(which can represent ~1530dB full-range, or just the 24bit sign+mantissa
144dB). With floating point arithmetics you can safely exceed 0dBFS
during summing (as long as you lower the signal before it is converted
to analog). Also the quantization noise when you apply gain-changes is
completely negligible or zero.
You can conveniently record tracks at, say, -30dBFS or -20dBFS (plenty
of headroom, no risk of clipping on the input) and don't bother about
the noise-floor or artifacts when summing.

In short: there's no need for external summing gear and most of it is
just snake-oil.

One valid case for using some external gear for summing is to add
non-linearities (and noise). Same reason why some guitarists prefer
Tube-amps. Although there do exist some quite good plugin emulations or
modeled channelstrips for "analog warmth". YMMV

While not directly relevant to summing, I highly recommend to spend
20mins on https://xiph.org/video/vid2.shtml  It's one of the best
explanations of bit-depth, dithering and overall basic concepts every
audio-engineer should know.


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