View Full Version : Question to Peter Roos about true stereo setting
09-28-2006, 12:05 PM
Peter I read many times your comments in threads about the "True stereo" concept. So you seem to be the man of the situation.
I tried the "true stereo reverb insert" setting in Pristine Space with an IR file. The IR was a stereo file. Should it have a difference if used on true stereo preset instead of normal preset?
Oddly this stereo IR used in each channel within the "true stereo reverb insert" setting appeared to give less stereo characteristic and more telescopic (read more depth) feeling !!! And it's more fluid, clear and rich. Could it be because the samples used are onstage (already panned and instruments positionned) ones ?
Should I give call to my psychologist or my feelings are not wrong ?
09-28-2006, 01:32 PM
I am actually a psychologist! Trained to do perception research, even...
(but I have been always working in the IT sector).
It is (or should be) simple.
True stereo requires FOUR impulse responses, not two...
Imagine you put two speakers on a stage, representing the sound of the orchestra, in stereo.
Now imagine two ears as mics (yours?) somewhere in the hall.
If you would now want to capture how the full stereo sound arrives at your ears, using the speakers as "orchestra", would a single stereo recording work? Yes if you want to re-record the sound emitted by the speakers. But no, if you want to record, or re-construct, how the signal from the left speaker arrives at each ear, as well as how the signal from the right speaker reaches your ears!
You will need a stereo (or two channel) recording for the left speaker and another stereo recording for the right speaker. Think of this as a matrix, two emitters, two mics.
So true stereo requires two stereo IR's, or four mono IR's.
A single stereo IR will only give you the results as if you sat in the hall with a true mono source. That's why I always say: with a single IR (two channels) you need to "mono-ize" the input, just like with the cheaper reverb boxes.
If you don't, instruments off-center, like the French Horns and the Contrabasses will only get a reverb/ambience at their location, not "all around".
Another way to explain this, is to say that in the convolution process there is no "stereo". Each channel is treated by ONE IR. Sounds from one side are not processed by the IR for the other channel.
To wind up, for true stereo IR applications, you need ONE stereo IR that contains the ambience information for sounds from the left, and one IR for sound from the right. The Altiverb people often call this "Quad", quite appropriately.
The easiest way to prove this for yourself, is to load a single stereo IR into your plugin, and to play a sound panned entirely left or right. You will be very disappointed about the result...
So either "mono-ize" the signal on your reverb bus, or use two (corresponding) stereo IR's with a true stereo setup. Using the same stereo IR twice will not work of course...
Mail or reply if you need more assistance.
09-28-2006, 10:43 PM
...how the signal from the left speaker arrives at each ear, as well as how the signal from the right speaker reaches your ears! You will need a stereo (or two channel) recording for the left speaker and another stereo recording for the right speaker. Think of this as a matrix, two emitters, two mics. So true stereo requires two stereo IR's, or four mono IR's. Kind regards, Thanks Peter you are a good psychologist, you should open a clinic for ear desorders ! If we take a hard left panned instrument on stage, the true stereo preset used in Pristine space works something like this: Instrument hard left position on stage directed to channels 1 and 2 Channel 1 (Higher audio level) and channel 2 (Lower audio level) Channels 1 and 2 receiving instrument output One Stereo Ir file for channel 1. One Stereo Ir file for channel 2 More reverb processed in channel 1 (Higher audio level) The wet output from channels cross together. Ears receive the direct dry flat part (no crossing) and the crossed wet part which make the feeling of depth (I left channels 3 and 4 apart to keep the picture simpler.) It's something like the binocular vision. In conclusion, using the true stereo preset with one IR stereo file in channel 1 and one IR stereo file in channel 2 is better than using one IR stereo file for channels 1 and 2, right ? Thanks Peter SergeD
09-28-2006, 11:24 PM
I believe, if I am not mistaken, that by using the above mentioned method by Peter (two stereo .wav) setup, "true stereo" allows you to place things anywhere in-between the stereo set, as opposed to being "locked" into postition. Granted, you can simulate this effect somewhat with panning, dry/wet mix on each channel and so forth. But a "true stereo" set offers pretty close to real placement.
Peter, please feel free to shoot me down on this - I might be totally off the mark.:o
09-29-2006, 12:32 PM
The true stereo option is a real advancement. Compared to the old fashioned way of acomplishing the same thing. In software it might have involved 2 stereo plugin instances. In hardware, it often took 4 processing engines. Or a stereo box dedicated to each channel. I used to do it in a daw recording effects to 2 stereo tracks in 2 passes, one for each channel.
Brian: I try to use an ir dedicated to each source position or zone. If I pan a source or bus to a different position, I'd use a different ir. But then again, I go for clarity of imaging rather than effect, so I tend to avoid doing things like panning frozen ir effects tracks. I mean I might do that as a temporary expedient during a mixing session. But I'd come back in and regen the effects tracks with the matching ir before doing the final cut. The cool thing about modern ir libraries is that they come with so many source positions.
09-29-2006, 08:03 PM
:wow: that true stereo thing is great. I feel now I belong to the big league !
It's so real and alive, it's all around like an envelop, I would say ambiophonic. My small yorkville monitors never shined this way. The frequency range is enlarged too. More sparkle, brilliance... yahoo...
Sorry, I digged so hard to find the good reverb setting then last week I got out of the hole in China ~|
I will now experiment by putting a second reverb layer.
Thanks Peter for talking and talking and talking again about True stereo in threads for years )(~
09-30-2006, 04:32 AM
Thanks for the kind words! :|:
Glad my reply was understandable and useful.
Please do experiment with ambience and reverb as much as you can.
One tip: don't send the same signal into two reverbs in the sense that you want to layer two reverbs... The ER's from both will thicken the sound too much and you will lose openness and clarity. But do try to use different reverbs for instruments in the front, middle and back.
Another trick to experiment with is to also add a short delay for each brass group (horns left, other brass right) and send that delay to the opposite (requires two busses). Then make a send (not too loud) from these busses to the reverb bus for the brass. With this you can create a subtle slap back echo (as if it were the first ER coming from the opposite wall). First make some calculations for the correct amount of delay. And make the delays slightly different, as the horns are playing with their bells point left and the other brass is playing in the direction of the audience (apart from the tuba of course).
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