"Froth"

[dirkwright]

Over the holidays I was listening to a lot of music both live and recorded. I noticed something I call "froth" "on top" of the music during loud passages. The amount of "froth" was directly proportional to the loudness of the music. I asked my wife, who hears better than I do, and she hears it also. So, I know I'm not imagining something here. I apologize in advance if this has been discussed to death already. Froth sounds like some kind of noise on top of the music. It's exactly like a head of foam on beer, as best as I can describe it. For years I thought it was just microphones or equipment overloading, but since it happens with live music then that can't be the case. Maybe it's just my ears overloading? Anyone else experience this?

 

[JohnRoberts]

Perhaps IM distortion. Circuit linearity degrades at high levels. For a pure tone this generates higher frequency harmonics, but for complex music this creates intermodulation products that occur anywhere in the audio band at higher and lower frequencies. This is easily identifiable on loud cymbal crashes as mud or non musical LF content correlated to the cymbal hits.

There may be some subtle different phenomenon associated with digital compression, but it could just be old fashioned IMD.

JR

 

[dirkwright]

OK, but how do I account for it for live music?

 

[JohnRoberts]

I have heard at least one of my ears distort at loud levels. If you get really really loud the air distorts, but your ears would be bleeding before the air distorts (air can't be squeezed and stretched the same amount at extremes).

Live music with no amplification? Even musical instruments may change their sound character when played loudly, just like our voice changes between soft and loud.

JR

 

[dirkwright]

Well, the live music was being recorded, and there were a couple of small speakers on the sides of the church, but I doubt much sound was actually coming from them. I mean, trumpets and choir can be really loud!

So, maybe it was just distortion from the sound equipment, I don't know, but it's in almost all of the recorded music I listen to. The loud passages have this froth on top of the sound. Have you heard it?

 

[JohnRoberts]

Simple.. do you hear distortion just on the recording or in the live room while tracking too?

Yes wind instruments change their sound character a bunch with how loud they are played. A flute only makes pure tones when played pianissimo (soft). Playing flute notes louder introduce more harmonics, and sonic complexity (not distortion per se).

JR

 

[dirkwright]

Simple.. do you hear distortion just on the recording or in the live room while tracking too?

Yes wind instruments change their sound character a bunch with how loud they are played. A flute only makes pure tones when played pianissimo (soft). Playing flute notes louder introduce more harmonics, and sonic complexity (not distortion per se).

JR

Well, I heard it both live and recorded. I'm not a recording engineer so I don't have much chance to compare live to recorded sound. Also, I don't recall the last time I heard unamplified live sound.

The froth does not appear to be harmonically related to anything that the instruments or the voices were doing. It's just some kind of noise, like a head of foam on a glass of beer.

 

[Kingston]

I apologize in advance if this has been discussed to death already. Froth sounds like some kind of noise on top of the music. It's exactly like a head of foam on beer, as best as I can describe it. For years I thought it was just microphones or equipment overloading, but since it happens with live music then that can't be the case. Maybe it's just my ears overloading? Anyone else experience this?

I think I know what you are hearing, too. Might be some kind of artifact of the way our ears work. I hear it on certain types of music with loud congested passages, and especially on live music with complete shite acoustics, as if the ears are resonating with it. It's a different sensation to hearing unbearably loud sounds.

Most recently I've noticed it trigger when our kid is crying. It's almost as if the ears are physically reacting to that type of timbre.

 

[dirkwright]

Yeah, there is no pain or other sensation associated with "froth", so I don't think it's because the music is too loud. My ears are not ringing afterwards either. The froth becomes greater with loudness and starts at even mid-loudness in my experience, and I can't even hear that well. It could very well be just really bad acoustics, but I hear it on professional recordings as well so I don't really know. The church did have bad acoustics. The walls were all really hard reflective surfaces, for example.

A good example is Carmina Burana O Fortuna. If you can find an uncompressed recording, the difference between the soft and loud passages makes "froth" very easy to hear.