[Ardour-Dev] a3: Normalise

[Sakari Bergen]

On 03.11.2010 05:54, Patrick Shirkey wrote:
> On Tue, November 2, 2010 1:21 am, Sakari Bergen wrote:
>> On 02.11.2010 06:25, Patrick Shirkey wrote:
>>> On Mon, November 1, 2010 7:59 am, Sakari Bergen wrote:
>>>> On 01.11.2010 14:43, Patrick Shirkey wrote:
>>>>> On Fri, October 29, 2010 3:10 pm, Sakari Bergen wrote:
>>>>>>      Hi,
>>>>>>
>>>>>> The export normalize ony adjusts the overall volume, so that the peak
>>>>>> value is as high as possible without clipping. Any other effect is
>>>>>> probably due to psychoacoustic phenomena (e.g. equal-loudness
>>>>>> curves),
>>>>>> or some non-linearities in your playback chain.
>>>>>>
>>>>> I was working with this in mind so I exported a couple of mixes. You
>>>>> can
>>>>> really hear the difference in these two files.
>>>>>
>>>>> The first is with the normalise enabled.
>>>>>
>>>>> http://djcj.org/audio/kotau/abundance/Abundance-Ambient-Psy-Trance-DJ_Kotau_Session_2010-10-31.flac
>>>>>
>>>>> http://djcj.org/audio/kotau/abundance/Abundance-Ambient-Psy-Trance-DJ_Kotau_Session_2010-11-01.flac
>>>>>
>>>>> I will stop using that feature for now as it is affecting the levels
>>>>> too
>>>>> much for my liking.
>>>> I challenge you to import these two files into Ardour (onto two tracks)
>>>> and invert the phase of the other track to hear the difference between
>>>> the files. By adjusting the level of one track about 1.5 dB, the tracks
>>>> should cancel each other out. It will be hard to hit the exact right
>>>> level for total cancellation, but you should notice, that nothing
>>>> stands
>>>> out from the difference signal.
>>>>
>>> I am happy to run this test.
>>>
>>> Apart from confirming what you have written above what would be the real
>>> world application of such data?
>>>
>>> For example if I export the track and then normalise it against say 10
>>> other tracks will that change the bass/high levels as significantly?
>>>
>>> Otherwise I think it is a useful feature but just not working out for me
>>> with this mix.
>>>
>>>
>>> Cheers.
>> All I'm saying is that the qualitative effect of normalizing is the same
>> as turning the volume dial in your playback system. Please see
>> http://en.wikipedia.org/wiki/Equal-loudness_contours for why you
>> perceive a difference in bass/high levels.
>>
>> The only time this is not the case is when the mix clips before
>> normalizing, in which case the clipping will be removed in the process,
>> by lowering the gain...
>>
> I think that it would be useful for you to compare the files as in this
> case  simply adjusting the volume of the second export does not result in
> the same  overall levels as the normalised export.

I did compare the files, but in a slightly different way (the outcome 
should be the same):
     1. Import both tracks into audacity
     2. Select a region in time where the unnormalized track does not clip
     3. Trim to that region
     4. Invert one of  the tracks
     5. Adjusting the level of one track produces almost complete 
cancellation (so far the same as what I described last time)
     6. Use Audacity's normalize on both tracks
     7. Playback and notice nothing is on the outputs

Part 2. is critical, because if you select a part where the track clips, 
normalize won't do anything to it.
This also relys on the fact that you "trust" Audacitys normalize...

> As Paul mentioned it
> could be because the track is polyphonic but it might also be that there
> are some adjustments that could be made to the algorithm based on this
> data?
>
>
> Cheers.

I don't know what Paul mentioned or where, but the "algorithm" is this 
simple:
     1. Find the peak value of the _mixed down_ track
     2. Calculate a gain coefficient so, that the new peak value will be 
at the target level
     3. Amplify the entire track with the _same_ gain

I don't know what you would be adjusting here... Normalizing is a 
strictly defined operation, there is no room for interpretation on what 
should and what should not be done.

Br,
Sakari

>>>> Br, Sakari
>>>>
>>>>>> -Sakari-
>>>>>>
>>>>>> On 28.10.2010 04:32, Patrick Shirkey wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> How does the normalise function work in ardour3 exporter?
>>>>>>>
>>>>>>> I have noticed it made some decisions on the levels of some of my
>>>>>>> tracks
>>>>>>> that affected the overall mixdown. Particularly the vocal tracks
>>>>>>> seem
>>>>>>> to
>>>>>>> have been affected by lowering the volume or maybe the other tracks
>>>>>>> have
>>>>>>> been boosted?
>>>>>>>
>>>>>>>
>>>>>>> Cheers.
>>>>>>>
>>>>>>>
>

-- 
Sakari Bergen
050 3754859