David,
My main concern with them is that if you listen to those samples over a stereo in a room, you have the added delayed signal not only in the direct sound (which is what you're after), but also in the reflected sounds.
EDIT: I see you've edited your post. How realistic is it to not have many other reflections around the back-wall reflection?
My main concern with them is that if you listen to those samples over a stereo in a room, you have the added delayed signal not only in the direct sound (which is what you're after), but also in the reflected sounds.
EDIT: I see you've edited your post. How realistic is it to not have many other reflections around the back-wall reflection?
Last edited:
The problem with an ETC is how to identify low level reflections that are perceived as a group?
Whats wrong with just looking at the impulse response? Too little low level resolution? You could square the impulse response and take some time average (to get the energy), and show this data in dB. What time average? I would think that what you would want to do is HP filter the data at say 500 Hz and then use a 1 ms time window. This would clearly show those reflections that were in a frequency range to be of interest. I might even HP at 1 kHz. I just don't believe that reflections below 500 Hz are an issue with imaging.
Maybe this isn't possible. maybe the two things are so tightly coupled that you can't talk about them seperately.
See above.
The edit was to correct a spelling.
Many other reflections? Late in the time window there may be many reflections and confusion about direction, but if we consider, say, the first 10 reflections then the median plane would include floor, back wall and ceiling, maybe a rear double bounce. Picture the image model (what you see with the speaker in a room full of mirrored surfaces)
They should all be discrete and seperable.
People seem to be in denial about whether reflections are audible. Try this: have your significant other hold up a 2 ft square piece of reflective something. It can be a piece of plywood or foam core or a cardboard box. Put pink noise or interstation noise on one speaker and have your helper slowly turn the reflecting surface back and forth. When the angles are right you will distinctly hear the reflection. Try it with the reflector several feet to the side of the path from speaker to you, and also several feet beneth the path (just above the floor).
Let me know if you don't hear anything.
David S.
p.s. I've also done the opposite test with absorbers. A helper stood behind with 2 largish pieces of fiberglass. He could lower them or raise them at will. When lowered they were several feet either side of my head and in line to block the side wall reflections. They in no way blocked the frontal sound. Although the reflections from the side wall were never obvious, when they were subtracted the soundstage changed. It was more "just between the speakers" or anechoic in effect. Try it.
Not sure what you are referring to? How to make a group of successive low level reflections visible? Impulse response or ETC is blind to direction.
I stand corrected.
Wait... thats what I said: "An ETC is the log magnitude plot of energy (pressure squared) so it can come from the room impulse response. "
Not to get at Graaf's goat, but this:
from http://human-factors.arc.nasa.gov/publibrary/Begault_2000_3d_Sound_Multimedia.pdf
Drs. Olive and Toole found in a AES paper about small rooms and reflection detection(lost the link):
although they are similarly audible:
All the available evidence seems to be saying the same things in general.
Another thing, broad polar patterned speakers will have more issues with diffraction than narrow dispersion. IOW, they'll need a better baffle to have less diffraction. Narrower will have more trouble getting a horn/waveguide correct for low coloration. It's different trade-offs, and perhaps no ideal.
Dan
from http://human-factors.arc.nasa.gov/publibrary/Begault_2000_3d_Sound_Multimedia.pdf
Drs. Olive and Toole found in a AES paper about small rooms and reflection detection(lost the link):
although they are similarly audible:
All the available evidence seems to be saying the same things in general.
Another thing, broad polar patterned speakers will have more issues with diffraction than narrow dispersion. IOW, they'll need a better baffle to have less diffraction. Narrower will have more trouble getting a horn/waveguide correct for low coloration. It's different trade-offs, and perhaps no ideal.
Dan
I am not one of them and I am familiar with the pitch effect that moving the reflection point to and away from the speaker has. In normal situations the reflection points don't move, and the reflections are less noticed and the pitch may be filtered out.
I think my argument against the use of those samples as prove still stands. The delayed sound will be not only in the direct sound, but also in all reflections.
I'm not following that. The simulated reflections will be included in your playback room's own reflections if you listen to the simulations? Sure but you can listen over headphones if that bothers you. Surely, if you can hear the effect of simulated reflections in your live room that proves the point of their audibility. If you can't hear them in your live room I can claim the room is obscuring them.
Your room's reflections won't make the simulated reflections more audible.
Can you hear them?
David S.
both standards ITU-R BS1116 and EBU Tech3276 asks for reflections lower than -20dB measured with ETC filtered between 1 and 8kHz, those here at 5 and 10ms are too strong :
The real problem are the low level reflections that are perceived as one (see Toole "Sound reproduction", chapter 6.5). There's no way to spot them in an ETC.
Are we saying we don't need to deal with colorations if they are stationary? If a floor bounce puts a hole in speaker response around 200 Hz and voices are as a consequence thined out (vocal fundamentals cancelled) are we okay with that as long as it is time invariant?
Less noticed: yes. Inconsequential: no.
David S.
I can definitely hear the effect of those delayed copies in the files you uploaded. No disagreement there.
I'm a bit surprised you don't understand what I am trying to say. I'll try to make it clearer.
So the delayed copy in the sound sample serves to demonstrate the effect of a back-wall reflection. Play this sound through your system and what do you hear? First you hear the direct sound. In the direct sound you'll find the original signal + the delayed copy. Alright, your brain might think 'here comes the direct sound, followed by a back-wall reflection' (assuming you brain gets no clues that it is actually a delayed copy of the original sound).
Then comes for example the first lateral reflection of the nearest sidewall. In this first reflection you'll first notice the original signal. This is what your brain expects. It's a normal first sidewall reflection. But then it is followed by an unnatural phenomenon: there is an extra delayed copy! Where does this delayed copy come from?
This same copy of the original will be in all reflections, not just in the direct sound.
Don't you think this is problem?
Now what if we listened to those samples over headphones? What we'd get is the direct sound first, followed shortly by a delayed copy. With headphones there are no reflections, but you do get a delayed copy of the original. What should your brain distill out of this? How is this the same or even similar to listening in a room and hearing the back-wall reflection? I think if you wanted to do such a test through headphones, you'd have to use binaural recordings.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.