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Below 80 Hz in mono ?

Discussion in 'Hardware Lounge' started by Geof, May 24, 2007.

  1. Geof

    Geof New Member

    I had infos that some (a few ? almost all ?) recordings have their bass (below 80 Hz) recorded/encoded in mono.

    Is it true ?
    If yes, is it only for a few recordings, or almost all ?
    Is it true with CD, SACD, DVD-A, vinyl, or only the case with sound in DVD-video ?
    If it is true, is it mon below 80 Hz ? below 60 Hz ? Below 40 Hz ?

    P.S.: I do not talk about the non-capacity of the ears to locate bass below 80 Hz. I am really talking about the mono versus stereo recording of bass in records.

  2. DYohn

    DYohn Well-Known Member Donor

    Information below 80Hz (approximately) is non-directional, so it doesn't matter if it is mono or stereo it will sound mono to the human listener. This is, of course, absent room effects such as reverb. Whether any LF information is recorded one way or the other would most likely depend on the preferences of the recording engineer for any given recording.
  3. Geof

    Geof New Member

    That I knew. But my thought on this is if it is indeed recorded in mono, it will be better to to use only one woofer instead of two.

    OK. So it is not always recorded in mono. Is it more often in stereo ?
  4. LarryB

    LarryB Active Member

  5. Tom R S 4

    Tom R S 4 New Member War Zone Member

    I'm not expert, and I don't even play one on TV, but here are a couple of thoughts that are my understanding/beliefs:

    1) Bass has been recorded in mono because of the physical limitations of vinyl (probably could say shellac here, or even wax(?))

    2) My own somewhat unscientific experience shows that bass isn't really non-directional until closer to 55Hz. - I know you said not to talk about it, but I can't help it.
  6. Geof

    Geof New Member

    I would like to read the facts somewhere, or from a sound engineer mouth. Is the bass encoded always in mono, was encoded in mono, is sometimes encoded in mono ?

    If I remember it well, it is more around 80 Hz. You can sometimes locate the bass at lower frequencies, but it is because of the interaction of the sound with the room, eg you hear distorsion.

    It's OK this time :evil:

  7. Geof

    Geof New Member

  8. Geof

    Geof New Member

    I have posted my questions in the steve hoffman forum. Hopefully I'll have an answer soon.

    Edit: I did not post this message because I thought I wasn't getting any answers here. I asked the question at steve hoffman forum to have a complement of infos, and because steve hoffman is a well respected sound engineer.
  9. DYohn

    DYohn Well-Known Member Donor

    Geoff, in my relatively limited experience working in recording studios, bass tracks for music are mixed in stereo but tend to be panned to the center, making them effectively mono. But again this is at the whim and artistic intent of the recording and mixing engineer. In general, low frequency information is recorded in mono no matter what form it may take after mixing. For film soundtracks, there are usually at least four bass tracks: the LFE channel track which is in mono, the center channel and rear surround tracks which are almost always in mono, and the main music tracks which are in stereo or four channel. Depending on the material and on the mixing engineer and producer's whims, the low frequency information below 100Hz or so may be EQ'd out of the main and surround tracks and completely directed to the LFE, or not. There is no 100% uniform answer possible.

    Why do you ask?
  10. Geof

    Geof New Member

    Thanks David.

    ... sorry, but your two sentences seem to contradict each other, no ? :?


    Because some say that mono recordings are better played through one speaker instead of two. So, if low information is recorded in mono for the majority of recordings, maybe it would be better to have only one woofer separated from the main speakers (one sub) instead of two woofers on each two speakers.
  11. DYohn

    DYohn Well-Known Member Donor

    re: the apparent contradiction. What I mean is generally the bass, if it is recorded with a discrete microphone, is recorded using only one mic to one track, in mono. That one track can be split and doubled and mixed into stereo if the mixing engineer so chooses.

    I agree that genuine mono recordings tend to sound better played back via a mono system. But since most of us do not have such, a good stereo system set up properly can simulate mono pretty well. :)
  12. Geof

    Geof New Member

    Better understood now. Many thanks, David. :)
  13. Steve L.

    Steve L. New Member

    So, if I have the choice to feed 2 seperate woofers an independant stereo feed vs one mono feed, which one would be the ideal way ?
  14. LarryB

    LarryB Active Member

    Very interesting thread! Thanks Geof, David and all other participants.
  15. Tom R S 4

    Tom R S 4 New Member War Zone Member

    I found an article that includes this about low frequencies being recorded in mono for LP's.

    Taken from an article on broadcastengineering.com: "Subs in control" Mar 1, 2007 12:00 PM, BY BOB HODAS

    Here's the whole article: http://broadcastengineering.com/audio/broadcasting_subs_control/
    I'm not sure about some of what he says in the article, but it still is interesting.

    Edited to fix typo in web page name.
  16. DYohn

    DYohn Well-Known Member Donor

    Good find, Tom!
  17. Geof

    Geof New Member

    - If we have a mono bass signal mixed in stereo, is the right signal identical to the left signal ? Or is the mixing producing a different left and right signal so the resulting impression is the bass perceived at the center ?

    - If the right and left bass signals are indeed identical, so they are mono X 2, would the two signals interfere with each other in a deleterious way ? If it is the case, can someone describe the deleterious effects ?

    - And if the two left and right identical bass signal interfere with each other in a deleterious way, wouldn't it be better, just ideally, to have only one sub (active or passive, doing 80 Hz and down) well located between the speakers (these speakers doing 80 Hz and up) instead of two woofers on each speaker ? Again, I am speaking in a ideal situation, just for the sake of discussion.
  18. Saurav

    Saurav Active Member War Zone Member

    Any time you have more than one source playing the same frequency, you have the potential for comb filtering effects, which will lead to reinforcement/cancellation and cause uneven frequency response (peaks and nulls) as you move around the room. This applies for stereo drivers, side wall reflections, and so on. As you go lower in frequency, the wavelengths increase, so the 'physical size' of a null/peak 'space' gets larger. In other words, for bass frequencies you may have to move a few feet to get from a peak to a null, while for midrange it may be inches, and for treble it's probably fractions of inches. That's why the perceived effect of too many wall reflections is mostly a muddying/lack of clarity, because you can't really hear the individual peaks/nulls. For bass, your whole head could be in a peak/null for a given frequency, so you'll hear a boomy or a missing note.

    So ideally, IMO, it is better to remove the bass from your stereo speakers, and send it to a single subwoofer, located somewhere between your front speakers. The sub should also be time/phase aligned with the main speakers to the extent possible... this is made easier if it's located in the front/middle. But subs have other issues to deal with, and the ideal position for time alignment with the mains may not be the ideal position for reducing the effect of room modes, and so on. So you compromise - treat your room, move the sub, EQ out the peaks, etc.
  19. Geof

    Geof New Member

    Thanks Saurav.
    And yes, all choices are compromises. This thread is only for discussion.

    But some of my questions remain:

    - If we have a mono bass signal mixed in stereo, is the right signal identical to the left signal ? Or is the mixing producing a different left and right signal so the resulting impression is the bass perceived at the center ?
  20. DYohn

    DYohn Well-Known Member Donor

    It could be either. If the intention is to create a mono signal, then usually the same information is placed in both right and left channels. If the intention is to create depth or instrument placement, etc, then there may be a time delay, reverb or level attenuation added to one or both channels to create the effect.

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