Currently Being ModeratedOct 10, 2012 5:00 AM (in response to dradlin)Re: HD500 Dual Tones - Phase Cancellation
This has been researched in some depth by meambobbo
Yes it is phase cancellation caused by slightly different delays in the signal path, yes it sounds great in stereo and rubbish in mono.
There have been feature requests to enhance the mixer block to include the ability to include a variable delay and possibly a phase inversion, but this hasn't appeared yet.
The only solution identified so far is to add neutral effects that introduce a slight time delay into one path or other
see meambobbo's guide where he mentions this: http://www.foobazaar.com/podhd/toneGuide/wishlist
and a thread discussing in more detail: http://line6.com/support/thread/88099
Currently Being ModeratedOct 10, 2012 9:35 AM (in response to Rewolf48)Re: HD500 Dual Tones - Phase Cancellation
thanks for answering this reowolf. dradlin, i know it's a lot of info, but given that you seemed to notice this right off, it might not be too difficult to follow. for the end result, go right to the setlist i made. it has a lot of combinations that work well and can be used as a template. basically, EQ's and compressors often introduce delay into a signal and can be used with relatively tone-neutral settings on one channel but not the other to try to get them in phase.
note: i only compared cab/mic combinations, not different amps. That's an additional variable.
i find the tone of dual cab/mic tones is far superior to any of the single cab/mic offerings. I'm hoping L6 will implement a less DSP-expensive and difficult method of acheiving phase correction. Please send them feedback on this via the forms linked in the above threads.
Currently Being ModeratedOct 11, 2012 5:14 AM (in response to meambobbo)Re: HD500 Dual Tones - Phase Cancellation
Just thinking about this a little more - I am not sure that I really want to be able to manually adjust the delays; if I did have the option I would like to have an "Auto" setting.
Each processing block will introduce a delay, and that delay is probably fixed but might vary with a switch setting e.g. some of the flangers or chorus effects or just switching the effect on and off.
The delay for each processing block can be measured in "samples", so in Auto mode the sum of the delays on each path can be compared and the path with the shorter delay then delayed by the difference between the two to match the longer delay path.
The delay may be different depending on whether the effect is switched on or off, but it shouldn't be difficult to update it in real time.
The same principle can be applied to the phase as well - each processing block models a real device that contains a number of amp stages, some of which will invert the signal, but the nett effect along each path can be summed and the shorter path inverted if necessary at the same time as it is being delayed (because even a simple inversion is going to cost a tiny amount of time).
Just an idea - my electrical engineering days are a long, long time ago; it is all IT these days
Currently Being ModeratedOct 11, 2012 6:46 AM (in response to Rewolf48)Re: HD500 Dual Tones - Phase Cancellation
no, i agree - i've investigated this and that's exactly right.
the pitch glide is the craziest example. when you turn it on it's at a certain number of samples, but as you use it, the exact delay changes. so if it's at unison and there's 20 sample delay, then you move it up an octave and back to unison, now the delay might be like 30 samples.
the mid-focus eq also seems to have slight variation of its delay as you move the LP freq and Q.
i think the best case fix would be a system setting that can be set either to auto or manual or mixed. auto would behave as you describe - the two channels are automatically synced. manual is straight sample-based delays adjustible on either channel as i originally described. mixed would automatically update the values, but you could set it to be always at a certain amount out of sync.
i think all modes would be important because when mixing certain cab/mics, some people may find the comb filter effect to be pleasing, reducing some harsh high-end. So manual/mixed would be as valuable as auto to these people. and some people may even want to toggle effects on/off to engage/disengage the comb filter, so they'd prefer manual over mixed.