[Ardour-Users] Ardour 3.0 beta 1a - Plugin levels 6dB higher than 2.x

[Roger James]

On 08/12/11 16:34, Jörn Nettingsmeier wrote:
> On 12/08/2011 03:33 PM, Roger James wrote:
>> This may be a feature rather than a bug, but it is puzzling me. I have a
>> session set up in Ardour 2.8.11 on Ubuntu 11.10 to do Ambisonic UHJ
>> decoding. This uses instances of Tom Szilagyi's IR convolver plugin to
>> do the conversion of UHJ to B format. I have duplicated this session
>> using Ardour 3.0 Beta 1a. Using exactly the same level settings in the
>> Ardour mixer and in the plugins wet and dry settings, the overall level
>> coming out of the plugin and showing up in the mixer meters is about 6
>> dB higher than that which I get in 2.8.
>>
>> Has anyone else observed anything like this? Have I missed something
>> obvious in the new UI? Has anyone got any ideas what is going on? It
>> just does not feel right to me to have drop the wet level in the plugin
>> by -9 db to leave some headroom for the rest of the conversion process.
>
> haven't seen that yet, but i haven't been looking too hard. i've used 
> quite a few sessions which have an insert to an external convolver 
> (jconvolver in my case), and haven't noticed anything obviously amiss.
>
I only noticed it when I did an export and ended up with a load of 
glowing red max level meters in the mixer (makes it hard to miss!) which 
I did not get with the same levels set up in 2.8.
> as an aside, there is a UHJ decoder in recent releases of fons' AMB 
> plugin set. it uses IIR phase shifters instead of FIR hilbert 
> transforms, but it works ok and is easier to set up...
>
I had not seen that I will check it out. Thanks.
> btw, i didn't know IR could do 2->3 convolutions - what exactly are 
> you doing? UHJ in, WXY out?
>
See 
http://pcfarina.eng.unipr.it/Aurora/conversion_between_uhj_and_b.htm. It 
is basically reproducing what goes in a full UHJ decoder which converts 
UHJ to B and then decodes the B to speaker feeds. I am doing UHJ to B 
then using ambdec to decode to various standard ITU speaker layouts 
which I route back into Ardours master bus. I then export wav files from 
which I producing ac3 using aften. My next step is to experiment with 
shelf filters to see if I can improve the listening experience in a 
normal domestic size environment. The statement that "different shelf 
filters are needed when decoding the B format recovered from 2 channel 
UHJ than those used for 4 channel UHJ (and also again for native B 
format), is widely used in different places in the Ambisonic literature. 
I just wish I could find a simple explanation of what these filters 
should be!
>> By the way the multichannel export support in 3.0 is awesome for playing
>> with Ambisonics etc! Keep up the good work guys.
>
> it is :) i've been whistling happy tunes ever since i moved over to a3.
>
Roger