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[Helge A Bentsen]

To throw a slight curve-ball into the mix...

To me, an acoustically reflective room sounds fine at lower levels, but can turn to an awful mess if the levels are brought up a bit. To take an example I'm very familiar with, my living room has the speakers against one wall, and the sofa against the opposite wall. At sensible volumes, all is well. Turn it up, and the slap echo between the two walls becomes very obviously audible on snare drums, claps, etc. Anything transient.

I designed the speakers to be tolerant of relatively high power levels, so they're still acting linearly when the problems become audible.

However, if I go around with the measurement mic, the reflections are always there. It's only at higher levels that I notice them, which makes me suspect there's some filtering going on between my ears, which stops working above a particular SPL.


Following that, I'd suggest that any study into the precedence effect etc would be incomplete without introducing SPL as a variable.

Chris

I've observed similar things in every warehouse-demo I've been in. Listen to a speaker at low levels is usually ok, turn it up and you need Peltors.
My storage is just like that, concrete floors, walls, roof and very little soft things absorbing sounds. Road cases are deliberately not soft.
Just opening the loading bay door improves SQ.

[Russell Ault]

To throw a slight curve-ball into the mix...

To me, an acoustically reflective room sounds fine at lower levels, but can turn to an awful mess if the levels are brought up a bit. To take an example I'm very familiar with, my living room has the speakers against one wall, and the sofa against the opposite wall. At sensible volumes, all is well. Turn it up, and the slap echo between the two walls becomes very obviously audible on snare drums, claps, etc. Anything transient.

I designed the speakers to be tolerant of relatively high power levels, so they're still acting linearly when the problems become audible.

However, if I go around with the measurement mic, the reflections are always there. It's only at higher levels that I notice them, which makes me suspect there's some filtering going on between my ears, which stops working above a particular SPL.


Following that, I'd suggest that any study into the precedence effect etc would be incomplete without introducing SPL as a variable.

Chris

I've spent a lot of time pondering this since you posted it. What you described is something I've definitely experienced myself, but I was having trouble reconciling it with my understanding of the precedence effect, and I think I've finally figured out why:

I don't think what you're describing is related to the precedence effect. To the best of my knowledge (and in some fairly un-scientific tests I performed on myself) the precedence effect doesn't change significantly with absolute level (although relative levels are hugely important). Moreover, my guess is that the delay time of the echo you're describing is too long for the brain to perform fusion on it anyway, especially for something impulse-y like a snare hit (where I would expect precedence-based fusion to break down at roughly the 5 ms mark for most people).

Instead, my guess is that what you're describing is actually a form of reverberance. There are studies going back at least 20 years (Hase's "Reverberance of an existing hall in relation to subsequent reverberation time and SPL" is the earliest my brief searching found) demonstrating that, while reverberation (i.e. the, measurable, physical property of a room or sound) doesn't typically change with absolute level, reverberance (i.e. the psychoacoustic experience of reverberation) does. Basically, higher SPL produces greater reverberance, even though the reverberation remains the same.

Does that fit with your experience?

-Russ

[Mark Wilkinson]

I've spent a lot of time pondering this since you posted it. What you described is something I've definitely experienced myself, but I was having trouble reconciling it with my understanding of the precedence effect, and I think I've finally figured out why:

I don't think what you're describing is related to the precedence effect. To the best of my knowledge (and in some fairly un-scientific tests I performed on myself) the precedence effect doesn't change significantly with absolute level (although relative levels are hugely important). Moreover, my guess is that the delay time of the echo you're describing is too long for the brain to perform fusion on it anyway, especially for something impulse-y like a snare hit (where I would expect precedence-based fusion to break down at roughly the 5 ms mark for most people).

Instead, my guess is that what you're describing is actually a form of reverberance. There are studies going back at least 20 years (Hase's "Reverberance of an existing hall in relation to subsequent reverberation time and SPL" is the earliest my brief searching found) demonstrating that, while reverberation (i.e. the, measurable, physical property of a room or sound) doesn't typically change with absolute level, reverberance (i.e. the psychoacoustic experience of reverberation) does. Basically, higher SPL produces greater reverberance, even though the reverberation remains the same.

Does that fit with your experience?

-Russ

I've been pondering the variables in this thread too.  I think there are several different things being kicked around.

With regard to sound going non-linear indoors when volume is turned up, I think that is due to differences in the time it takes for frequencies to decay across the spectrum, like in RT-60 measurements.  Unless in a room with super solid walls, ceiling, floor... bass absorption is invariably greater than high freq, and the resultant unpleasant tonal shift occurs from relatively longer lingering high freq reverb.

I'm thinking slap echo, etc, heightens the tonal shift and muddiness further, because i saw Don Davis say on a SynAudCon video, that the Haas effect keys off peaks.
That it's peaks tied together, not just a general time window for all equal level frequencies.  He said if a string of peaks occur within 20ms each, the Haas effect can be extended on and on.    Which sounds like echo slap ear bleed to me 

In circling back to phase audibility itself, I don't think either RT-60 room problems, or the Haas effect have anything to do with it.
I mean, RT-60 differnces are an acoustic issue. 
And Haas is more strictly defined/measured for the ear's integration of identical sounds, than for complex music.  For clicks, wiki says it's under 5sec , but for music It appears to turn into a guessing range of up to 40ms, before it's heard as echo.
The clincher for me that Haas is a separate issue from phase audibility, is how I've heard single transients,... kick, snare, bell, etc.... sound considerably stronger/clearer after flattening phase.

Anyway, just a few more 2c thoughts...

[Art Welter]

I've been pondering the variables in this thread too.  I think there are several different things being kicked around.

With regard to sound going non-linear indoors when volume is turned up, I think that is due to differences in the time it takes for frequencies to decay across the spectrum, like in RT-60 measurements.  Unless in a room with super solid walls, ceiling, floor... bass absorption is invariably greater than high freq, and the resultant unpleasant tonal shift occurs from relatively longer lingering high freq reverb.

Mark,

High frequency absorption is usually greater than low frequency in most domestic size rooms, and in large halls the audience can provide HF absorption, but has less effect at low frequency.

That said, the experience of short reverb times sounding benign at lower levels, but progressively "sounding" worse as level is increased seems not to be RT-60 related, but due to the way our hearing works- the echos are perceived more as "noise" at louder levels.

I'll provide a quote from the "King of Reverb", (30+ years with Lexicon) David H. Griesinger, to explain:
 
"The basilar membrane divides sound pressure into more than 40 overlapping channels, each with a bandwidth proportional to its frequency. So a critical band at 1000Hz is inherently capable of carrying ten times as much information as a critical band at 100Hz. Indeed, we know that most of the intelligibility of speech lies in frequencies between 700 and 4000Hz.

At the vocal formant frequencies each basilar membrane filter typically contains three or more harmonics of speech or musical fundamentals. These harmonics interfere with each other to create a strongly amplitude modulated signal.   Modulation depth of those frequencies are large, and the peak amplitudes align in time. The modulations in the signal are detected linearly by the hair cells, but the nerve firing rate for time variations longer than about 20 milliseconds is approximately logarithmically proportional to the sound pressure. The brain stem separates these modulations by pitch using a number of comb filters each ~100ms long.  The filters detect pitches using the travel speed of nerve pulses in tiny fibers.
Once separated by pitch the brain stem compares the amplitude of the modulations for each pitch across the critical bands to determine the timbre of the source, and compares the amplitude and timing of the modulations at each pitch between the two ears to determine sound direction. Using these cues the brain stem assembles events into separate foreground sound streams, one for each source. Sound left over after the foreground is extracted is assigned to a background sound stream.
Reflections and reverberation randomize the phases of the harmonics. When the reflections are too strong the modulations in each frequency band become noise-like, and although pitch is still detectable, timbre and direction are not. "

Anyway, that seems to be a far better explanation than anything I came across before, and I did spend quite a few decades thinking about the cause of it before coming across the above in David's "The audibility of direct sound as a key to measuring the clarity of speech and music".

Art 

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