18 thoughts on “Tech Talk: Panning Around

  • March 4, 2015 at 5:53 pm

    Mark this is good stuff. Especially for a guy who is wondering how to setup a home sound room. I say sound room because I am not yet sold on the benifts of 5 speakers.

    • March 5, 2015 at 1:42 pm

      Scot, before you setup your room you should visit a friend or a high-end retailer and check out a proper 5.1 surround music system. Take some files or a disc of music that you like in 5.1 surround, listen and then decide.

  • March 4, 2015 at 6:14 pm

    Yes, there is a lot of misunderstanding and mis-information on the subject of subwoofer set-up. I have been to “THX School.” I have set up dozens of HT systems. The test tones, etc., won’t really help, and I wouldn’t “delay” your sub 1 ms, it’s already the ‘slowest’ speaker you own.

    Put on familiar music that has powerful, extended bass lines and LF events which have true”start/stop” transient qualities. Set your speakers and sub up to deliver A-grade performance on musical bass transients that give pitch, attack, and definition to these usually muddled notes. Remember, organ pedals stop and start too, and precision low frequencies make this obvious and startling, as occurs in real life.

    If your system is properly balanced at that point, get out your movie material and see what you hear on LFE passages; if you like a little extra “hot fudge” on your HT sundae, go ahead, but do not lose the qualities needed for precise reproduction of musical bass transients.

    • March 5, 2015 at 1:44 pm

      Subwoofer and the amount of low frequency energy is very tough to get right…especially since the amplifier is in the SUB and not in the AVR. We do align our subwoofer output using a sound pressure meter because our mixes have to translate to other rooms (specifically move theaters) and they count on correct levels.

  • March 4, 2015 at 7:43 pm

    Actually, Mark, your correspondent is correct about the correct level of the LFE signal. The LFE is not the same as bass management. The sub handles both jobs, but they are conceptually distinct and can be set independently.

    LFE stands for “Low Frequency Effects” and was introduced by the movie industry not for faithful reproduction of music but for the loud bangs and booms in movies. It’s the “.1” track. The LFE track is deliberately mixed 10db low to allow headroom for the loudest sound effects. It has to be boosted by 10db on playback for precisely that reason.

    The sub does double duty, however. It not only carries the LFE but also the sounds below 80hz from the surrounds and often the front three speakers as well. The standard crossover point for bass management in movies is 80Hz, a standard promulgated by George Lucas as part of the THX calibration of movie theaters. Anyone setting up a home theater will most likely use that crossover point for compatibility with movies.

    The rule followed by AV Receivers is to boost the decoded LFE signal from the soundtrack by 10db. There’s no similar rule for the redirected bass, which is more often adjusted “to taste.” As a mixing engineer, your insights into panned signals is applicable to the redirected (or “steered”) bass, but the LFE 10db cut and boost is a different matter.

    This same schema is followed by Dolby and DTS. The exception is SACD, which, not being a movie system, does not boost its .1 signal, since it’s not really an LFE signal but part of the music, and thus doesn’t get the reciprocal 10db cut and boost. (And in fact, many multichannel classical recordings are in “5.0” – no subwoofer signal other than your own bass management.)

    Anyone who uses the multichannel analog output of a disk player to connect to an AVR has to make these adjustments manually in the AVR, since it’s not doing the decoding and can’t know what the encoding was. It has to be done in the AVR because if you boost the .1 output inside the player, you’ll likely overload either its output stage or the AVR’s input.

    And if you’re running that way, setting the LFE level manually, SACDs will sound boomy until you remember to cancel the 10db boost to the sub!

    • March 5, 2015 at 1:47 pm

      Thanks Phil…based on several comments and emails, I’m still looking in the topic. Your explanation is quite good. I think my wording of the LFE channel was part of my mistake. I don’t mix LFE for movies, my mixes have a “boom” channel output from my console that is not bass managed and is not attenuated.

      • March 5, 2015 at 6:43 pm

        Mark, since the 10db boost applied by AVRs that do the decoding themselves is hard-wired and can’t easily be changed by the consumer without turning down the total signal to the subwoofer, drastically cutting the volume of the steered bass, you may not *want* to apply attenuation to your .1 channel in making your disks but you *have* to.

        It doesn’t matter if you use Dolby TrueHD, DTS HD Master Audio, or LPCM – the AVR will always boost the .1 channel by 10db unless there’s a configuration setting on sub obscure menu to undo that 10db boost.

        So if you don’t attenuate your .1 channel it will in most cases come out too loud because the AVR will boost it because it’s a non-SACD “.1” channel and that’s what the specification directs for all codecs other than SACD.

        Why not try A/Bing the original mix of one of your Blu-rays that has significant activity on the .1 track and the playback of that disk by one of your Oppos. If the playback sub sounds the same in relation to the rest of the speakers, I’m wrong. If it sounds a lot louder, I’m right.

        You’re one of the few folks who could actually easily run such a test!

        • March 5, 2015 at 7:01 pm

          It just occurred to me that DVD-Audio, which (like SACD) was designed for music, not movies, may not apply the reciprocal 10db cut-and-boost to the .1 channel.

          On the other hand, from what I’ve heard, TrueHD is based on DVD-A. Whether it had to add the cut-and-boost or whether DVD-A already used it I don’t know.

          But when you use Blu-ray as your distribution medium, it comes with the territory.

        • March 6, 2015 at 6:35 am

          I’m digging in to this..and learning. I can do the test you’re suggesting. Stay tuned. From what I hear right now, I don’t lower the sub channel and the mixes sound correct.

  • March 4, 2015 at 8:43 pm

    The LFE channel might be a good idea for movie sound effects, but it doesn’t let music sound natural, at least not with my sound system. I prefer to connect my subwoofers (yes plural) to the front speakers and turn off the LFE channel. Music sounds better this way. I adjust all the surround speaker levels using pink noise and a real-time analyzer with A weighting with the subwoofers off, and I adjust the gain of the subwoofers using pink noise and a real-time analyzer with C weighting. Some early DVDs came with surround alignment programs and I don’t remember them as being that useful. Is there a better way?

    • March 5, 2015 at 1:50 pm

      Dick, I think you’re losing the information in my .1 channel, which has meaningful amounts so very low bass. My own calibration disc has uniform levels on all outputs because my discs don’t get the usual lowering and raising of the .1 channel.

  • March 4, 2015 at 11:40 pm

    Hi Mark,
    Thank you for addressing this subject. As most of my listening is in 5.1, it is a constant source of annoyance that different formats have different output levels for the LFE channel. SACD is always lower than DVD-A and DTS is different again. It is hardly surprising that surround has not taken off, when we have “format wars”, stereo audiophiles claiming (falsely) that it is a gimmick and the lady of the house not only objecting to five speakers, but wondering why you can’t have the two you already own put behind the curtains?

    • March 5, 2015 at 1:51 pm

      Handling low end signals is a constant struggle. But even without a subwoofer speaker, surround trumps stereo.

    • March 6, 2015 at 3:44 pm

      Put your foot down and let her know the listening room is your man cave and your the designer there. Ask her to go to the kitchen and make you something to eat while you set up the 5.1 system.
      As B B King sings, “As long as I payin the rent and the bills, I payin the cost to be the boss!

  • March 5, 2015 at 3:15 pm

    Hi Mark,

    If I’m understanding your correctly, then, your are lowering the LFE material by 10db on your discs. So wouldn’t the material contained in the ‘.1’ LFE channel on your discs be 10db too hot if played through a processor that is bumping the level by 10db?

    • March 6, 2015 at 6:32 am

      I don’t change the level of my bass output channel…it’s the “boom” channel on my console. I’ll be going through the exact procedure…including the encoding method in future posts.

  • March 6, 2015 at 6:02 pm

    I can hear my subwoofer only by cranking it up to near-maximum — otherwise, my five to seven full-range speakers pump out all the bass available on any given disc or download. It’s so pointless and redundant that I’ve had it unplugged for well over a year — its only purpose now is to act as a table for my tiny AVR control monitor.

    Modern AVRs can do a low-pass filter and send the bass to the subwoofer for folks with puny satellite speakers, so it makes more sense when labels don’t even bother with the subwoofer. And, in fact, most labels go with 5.0, not 5.1 or 7.1.

    • March 8, 2015 at 7:26 am

      Not sure you’re right here…of the surround music discs that I’ve surveyed, it’s the exception that doesn’t use the subwoofer.

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