Re: [LAU] master levels

On Sun, 1 Feb 2015, Brent Busby wrote:

> Ardour is doing 32-bit FP math to handle samples internally.
>
> And yet, when I change the volume on the master fader, even if I

Which master fader? The one in Ardour or the one in ALSA?

> compensate for the volume change on my RME Multiface's physical volume
> knob for the headphone monitor, I'd almost swear I can hear some sort of
> change in the audio. I'm not using any post-fader plugins. I'm
> probably just fooling myself, but is it possible to change the perceived
> audio by just changing the output level over a 4-5db range when you've
> got a precision like Ardour is using, and you're listening through
> decent 24-bit converters?

Ardour's steps (around 0db) are very small, sometimes as many as 4 step
for each .1db. (ctl/alt/mouse wheel or send MIDI pitch wheel in MC mode)
ALSA's step are a lot grainier. (my ice1712 with mudita24 is .5db steps
and Qasmixer gives 1db steps)

> In a related question (which was the real reason I wanted to know), what
> kind of levels should we be shooting for in the master output anyway?

I have heard -6 to -3.

> Of course, in the old analog tape world, they used to shoot for zero,
> maybe a little hotter if you wanted some saturation. In digital, they

With FP, it is possible to go over 0 :) but not suggested.

> say mix to about -3 or -4db. And mastering houses seem to want more
> headroom than that (-6 or 7db), even though in priciple, with 24-bit
> resolution, they could just adjust it themselves without changing it
> timbrally (true?). Why do they care what your maximum level is as long
> as it's 24-bit and it's not clipping?

6db down is one bit of 24... to go to 16 for a CD means cutting off bits
on the bottom (maybe adding some noise) so -6 is safe.

> Commercial CD's these days seem to be mastered with the idea that if the
> level ever fell below -1db, that would be a sin against God.

This depends on your audience. This is not always the end listener, but
may be the broadcaster or distributor or whoever is paying for it.
Dynamics are nice IMO.

> I suppose the question I'm wondering is, if you've got it just the way
> you like it at some particular master fader setting, is anything harmed
> by making it a little hotter before you export, especially if you're
> going to be putting a track on CD where it will be only 16-bit? Or
> should you just keep it where it is, even if you're wasting some headroom?

Only 16 bit? High quality tape with noise reduction is 13 bit or so.

Try for yourself three mixes, one at -1 and one at -3 and one at -6.
Listen for the difference. Run them on more than one player at a time and
switch them with jack or a mute key and see if the slightly higher level
is worth it.

--
Len Ovens
www.ovenwerks.net
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