Originally Posted by Floyd Toole
That done, with smooth non-resonant bass, the overall spectral balance is a moving target. Many people for movies like significant boost for impressive sound effects, others are more moderated. For music, the circle of confusion is very obvious and some cuts are mixed - especially a lot of great older material - with insufficient low bass. Sometimes there simply is nothing there to boost - 30 ips analog tape has little or nothing below about 50 Hz. Other material was obvious mixed for, as I call them, the bass-deprived masses, and turning the bass control down is a tasteful action.
Or you can make one setting and take it as it comes. For me one setting does not fit all programs. The problem is that tone controls in digital gear are sometimes a pain in the butt to operate - not like old fashioned knobs :-(. So sometimes I just get lazy and put up with it.
I think most of this is variation in bass level is purposeful rather than necessarily "circle of confusion". In most acoustic music like orchestral music, bass tends to be naturally weak and heard mostly in the reverberant field anyway. The exception might be large drums. I've heard it said that orchestras always struggle to recruit enough players for the string bass section because it's just never loud enough.
I reckon that subtlety in the bass is just what people were used to in days past.
That all changed over the last several decades with the evolution of music to rock-and-roll and then to various dance (starting with disco) and electronic forms, and of course, subwoofers were invented. Before long, entire music genres arose that were oriented around bass (drum and bass, ambient/dub leading to dub step) and these styles fed back into the popular music of today.
Today's masses are very much bass deprived. Just look at some of the subwoofer systems people build over the in the DIY sub-forum
. Even I'm running a measly 4 x 21" (high output / high excursion) sub system powered by 12 kW. At least my needs for music and for movies above 20 Hz are taken care of, but I could definitely use more below for the movies.
The important consideration when evaluating bass levels in a recording (and/or on a playback system) is how the fundamental tones in the subwoofer range balance out with the harmonics. Many people run their subs too hot (not always intentionally) so that the fundamental overwhelms and masks the harmonics. This can cause instruments like the string bass to lose their timbrel character and harm intelligibility of the rhythm and tone, even when resonances are adequately controlled. The resulting sound can be very slow sounding. It can even paradoxically make the bass sound quieter. Too little sub, on the other hand is thin and lacks weight and depth. Transient response can also be poorly defined with too little sub.
In the above respects, I find bass level to be fairly consistent between tracks. (There are always exceptions.) Sure, some tracks have bass that's a lot louder than on other tracks, but this appears to have been done in the mix with both fundamental and harmonics mixed hotter and not the fundamental alone.
Indeed, I find that in the purest sense, subwoofer bass isn't really loud, especially below 70 Hz or so. Almost all the loudness comes from the contribution of higher harmonics. The sound of the subwoofer is mostly weight and feeling. I didn't fully appreciate this until I upgraded my subs recently. I was surprised by how much I could crank them up and still not really hear them. I guess most subs output a lot of harmonic distortion, even at low levels, which gives them a characteristic sound. Most of the "sound" of the bass seems to live around and above 100 Hz, even for tones with very low fundamental frequencies.
About harmonic distortion, THD is a largely useless measure because the measurement is usually dominated by 2nd and 3rd harmonics, which are the least audible and least important. I believe it's the higher harmonics that are more important because they are *much* easier to hear at lower levels. Inter-modulation distortion is also probably very important and may correlate with transient response distortion. Most good subwoofer drivers use shorting rings and other strategies to limit effects from inductance non-linearity, which can cause a lot of this distortion.
Originally Posted by Floyd Toole
BTW, the discussions about reflections, imaging, spaciousness, etc. have been based on listening in pure old fashioned, directionally and spatially deprived stereo. Don't any of you employ upmixers? I know that some of the most popular ones are not optimum, usually too aggressive, but it is possible to manipulate the levels of surround vs. frontal energy, delays, etc. I'm just suggesting that it is so rewarding when it is "right" that I leave it on most of the time. The old Lexicon Logic7 in its full blown, adjustable, implementation was excellent, but those days are past. At the moment my Anthem processor has an "Anthem music" mode that is very tasteful, leaving the stereo soundstage pretty much alone and adding subtle surround envelopment. I will have to start again when I get my SDP75. I'm told that the Auro3D upmixer is good; we'll see. I find upmixing to be a nice addition to a lot of popular music and jazz, and it is especially rewarding for classical repertoire - getting me an important step closer to my visits to the LA Phil concerts. The beauty of upmixing is that it is not a permanent, built-in feature. It is flexible - it even has an "off" button. I suspect that much of the anxiety over optimum loudspeaker dispersion would fade if you were to get it optimized :-)
We need multichannel music, lots of it! With streaming the "format wars" are fading. Some video music concerts are a pleasure to experience in 7.1.
I actually used up-mixing via Dolby PL2x when I first gained the capability, but after I made improvements to my room and system, I stopped using it. I reached a point where my front left and right sounded so much better than the center and surrounds that the extra channels detracted from the sound quality. The front left and right also provided the envelopment and panning cues I heard in the surround up-mix and in a way that sounded more proportionate and realistic.
I did play with the optional controls a fair bit, but they weren't all that useful. Another thing I noticed with up-mixing is that the low frequencies changed a lot and not usually for the better. They generally sounded weaker in the up-mixed mode than they did in 2 channel mode. IIRC, it varied a lot by mix, which did not give me a lot of confidence in the system. A lot of this may have to do with the way Dolby attempts to maintain equal energy when it applies the dematrixing, but I don't know.
I may revisit this problem someday when I get more time and can experiment with my own algorithms, now that I have completely custom processing capability. That'll probably wait until I have good interactively adjustable tone controls though.