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Causes of Soundstage, Imaging, etc.

Discussion in 'Sound Science' started by tzjin, Jul 27, 2012.
  1. tzjin
    Hi guys,
    With this whole objective vs subjective debate raging on, I'd really like to educate myself to understand the objective side better. I understand the basics of frequency responses and transients, and how some components are theoretically indistinguishable to the human ear after a certain point.
    My question is more about what some may consider the more subjective descriptions of sound, namely soundstage (width, depth and height), imaging, and the perception of detail. I've heard the claim that all parts of sound can be objectively measured, so could someone please explain what causes these illusions of the mind? Graphs and pretty pictures would be great, but any help is appreciated.
    I'm also interested in how "spacious sounding" DAC's and amps affect the performance of the headphones plugged into them. Does the headphone itself need to be capable of throwing a large soundstage in order to take advantage of the benefits provided by the amp or dac? Or is the effect "cumulative", as in any improvement along the signal line will positively impact the soundstage experienced by the listener?
    Thanks in advance!
  2. Headdie
    Mind illusions you've said... It could be the answer...
  3. Arietites
    I think illusion is not the right term to use, it's not like optical illusions. If recording is well made and audio gear do the job well, your "brain" (not true in fact, a part called medial superior olive) will compute the location of a sound by interaural sound differences for example (differential time of arrival at both ears). Other mechanisms are used to reconstruct a 3D space of sound environment in your brain (auditory cortex).
    Techniques used in audio to exploit this... http://en.wikipedia.org/wiki/3D_audio_effect
  4. Headdie
    I guess he means that for two audibly transparent amplifier, some people will hear larger/higher soundstage or better imaging in one or the other.
  5. Arietites
    hmm... trolling a bit... everyone's brain is different [​IMG]
  6. bigshot
    Haha! I've been blocked from the Subjective thread. I guess we need to protect subjectivity in the sound science forum. I'm proud and happy to join you folks here in this thread. Hail fellows, well met!
  7. bigshot
    Soundstage is created by the combination of several elements. It's the space between the right and left channels, it's subtle psychoacoustic clues that indicate depth and it's a function of clarity, which is affected by frequency response and distortion. I'd be happy to share what I know about these areas if you're interested in any of them.
  8. tzjin
    I refer to it as an illusion, because though the sound is coming from right over/in your ears, you perceive it as coming from in front of or behind you, and at least a couple of feet away. 
    @Bigshot: Could you elaborate more on "psychoacoustic cues"? Not really sure what you mean there. Also about clarity. Is that related to having a short transient response? I'm sure there's probably more to it as well, hence my question about detail in the first post. If you ever get unbanned, we should talk more.
    On a side note, I'm not trying to defend subjectivity or attack objectivity. This is a simple search for answers. I'd love to hear from anybody, anywhere if they can explain things clearly.
  9. billybob_jcv
    I think you have to separate the effects caused by the way the miking & mixing of the original source was performed from the effects that are caused by the playback components.  I suspect it's not nearly as "subjective" as we might think - it probably requires analyzing how the the signals of the left & right channels differ from each other AND how those differences affect the pinna of the ear AND how that is then interpreted as "localization" by the listener.  That seems like it is pretty far from any of the typical measurements made for audio gear - I don't even know if anyone other than a binaural expert could really deal with it adequately.
  10. tzjin
    So it sounds like at the moment there is no definitive way of quantifying soundstage. From what you're saying, it appears that, by sending differing information the the right and left ears, you achieve a feeling space similar to that of 3d movies. Hopefully a binaural expert drops by sometime.
    Does the equipment used to play back the music really artificially add soundstage? I always assumed that the amplifier and DAC only served to recreate the soundstage, not add anything to it.
  11. billybob_jcv
  12. xnor
    tzjn, I recommend on reading up ITD and ILD (interaural time/level differences), head shadow, HRTF and further links regarding localization on Wikipedia.
    There are HRTF measurements online that show the differences in frequency response for different angles of the sound source.
    On a less theoretical note, I think that L/R imbalances in a headphone could cause a bigger perceived "soundstage", the former being something you don't want to see in an (expensive) hifi headphone.
  13. Deathwish238
    Illusion is a good word to use. Obviously, with headphones you cannot technically have a real soundstage since it emanates from directly beside your ears versus speakers which will allow for a true soundstage. Yet, there's no doubt that different headphones can have drastically different sound stages. It's not like our brain knows or cares if we're listening to speakers or headphones after all.
    I'm quite interested in being able to measure and predict a headhone's soundstage. The by far biggest factor I've seen is if a headphone is open or not, but just because a headphone is closed does not mean it will have a poor sound stage either.
    If you've ever played with Dolby Headphone in Foobar, it can create the impression of a bigger soundstage too. So it's definitely not something that is limited to your speakers/dac/amp, but also what your'e listening to.
    HRTF is interesting. However, it to me shows on axis vs off axis performance more than soundstage. Not that that means that on axis vs off axis performance has no relation to soundstage.
  14. Arietites
    Can someone explain me the physics behind this ? I  have heard many times that closed headphones have lesser soundstage compared to open headphones.
  15. xnor
    I agree with everything else you said. Off axis means that the speaker doesn't point directly to the center of your head, but this is not what happens in HRTF measurements. Typically a speaker is moved around your head always pointing at the center of your head. Measurements are taken every couple of degrees.
    I believe that perceived soundstage will be smaller if the headphones' frequency response matches the FR of sound coming from in front of the head closer than the FR of sound coming from left/right.

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