An article to the music industry by
D. Michael Shields
COPYRIGHT DMSI, INC. JANUARY 2012
For serious audiophiles, there seems to be a never ending search for just the right combination of things to make the "perfect" playback system. We even have a whole meta-language to describe the search.
and so on.
The "just right" combination seems eternally elusive. Certainly, if there is a "just right" combination, it's not for all recordings. In fact, many audiophiles will limit their most frequent listening to recordings which sound "right" on the system of the moment.
- This is the First "Wrong Thing". The purpose of music reproduction is to listen to the music. If you avoid certain music because of the sound quality, that is a real loss.
The search never ends. The "just right" combination of things includes the recording, the playback equipment, preamplifier, power amplifiers, loudspeakers, cables, AC mains power quality and other items. Also it includes the room, the position of things in the room, your mood, your hearing and your tastes and expectations. This is a long list of things that have to come together. The likelihood that there is a personal optimum solution is small. The likelihood of a general solution is zero.
- This is the Second "Wrong Thing". Eternally modifying and adjusting the system doesn't leave much time for listening to the music. Besides, you'll never get there and it will cost a lot.
Aside from the variables of your particular equipment in your particular room and your particular expectations, there may be an underlying problem.
First we have to dispense with problems which can be solved. Basic technical matters like signal-to-noise ratio, distortion and frequency response (at least in the electronics) are routinely solved even in good mid-market equipment.
Let's assume you have managed to put together a pretty good system to your taste, it's in a pretty good room and you're in a good mood. You put on a recording which you reliably enjoy and everything is nice. Then you go to a different recording and things are suddenly not so good. Maybe it's a little "thin" or "screechy" sounding or lacks depth or whatever. Your system didn't change, your room didn't change….maybe your mood changed a little. What changed was the recording.
This gets to the crux of the problem. The better your playback system, the more clearly you can hear (and often NOT enjoy) the properties of the recording.
If you have some recordings which sound really nice, and some which seem to have significantly skewed tonal balance, then one must be wrong. This begs the question of the definition of "high fidelity". Fidelity to what? In the context of consumer playback of commercial recordings, we can't go further upstream than the recording we are listening to. So our high fidelity must be fidelity to the recording, but not necessarily to the original sound. If you require fidelity to the original sound, you will have to go to a concert. Not only that, but in the case of many (most?) pop recordings, there is no original sound. The only "original" that ever existed was what came out of the monitor loudspeakers when the mixing was done.
But if our "high fidelity" to the recording produces a result we don't enjoy, why should we listen to it? What can we do about it?
Assuming the recording is free of gross defects such as hum, buzz, wow, flutter, distortion and data reduction, the biggest difference among recordings is the tonal balance.
The strongest determinant of tonal balance is the frequency response.
Adjustment of the relative loudness of low or high frequencies will strongly affect the tonal balance of music reproduction. That is why controls which perform such an adjustment are generically called tone controls. In professional audio practice, controls which adjust the frequency response are called equalizers, but this terminology has its roots in something other than what we are talking about.
Somewhere in the history of audiophile purism, tone controls got a bad rap. One argument is that the listener should not be "allowed" to modify the tonal balance chosen by the recording producer. Another argument is that electrical circuits which modify the frequency response are somehow "impure" and should be avoided on principle.
- This is the Third "Wrong Thing". The notion that we shouldn't allow ourselves to adjust what we listen to in order to maximize our enjoyment of the music.
If we accept the notion that our "high fidelity" can't reach further back than the recording, we are still confronted by the fact that the producer of the recording made decisions on a system different from ours, in a room different from ours.
And here we get to the aforementioned "underlying problem". Frequency response (technically: amplitude response vs. frequency) is the strongest determinant of tonal balance. Uniform (flat) frequency response is easy to obtain in the electronic parts of the signal chain. In the electro acoustic parts, microphones and loudspeakers, not so.
Frequency response in transducers is a truly complicated subject, but for our purposes it boils down to this: the frequency response of a loudspeaker cannot be specified independently of its radiation characteristics (dispersion) or the room in which it is operated. As a result, the usual on-axis free-field response of a loudspeaker tells us little about its perceived tonal balance in actual use.
In many professional monitor situations, the frequency response of the loudspeaker system at the listening position is somewhat tilted downward in the high frequencies. This has its origins in film sound and the so-called "X" curve used in cinemas. If musical content is mixed in this environment, the result will be too "hot" when it is played on a "flat" system. In this regard, many consumer loudspeakers are noticeably more accurate than many "professional" loudspeakers.
The result of this is a surprisingly systematic error in the making of recordings. Many, possibly a majority of studio-originated recordings, need to be somewhat rolled-off during playback in order to have a natural sounding tonal balance. This rolloff may begin as low as 2 kHz and amount to as much as -6 to -8 dB at 10 kHz.
- This is the Fourth "Wrong Thing". There is a systematic error in the way many recordings are made and its historical origins are clear.
Beyond the systematic problem of too much high frequency content there are other frequently recurring problems. One is particularly common.
Many microphones which are popular for vocal recording have a "presence bump" in the response around 5 kHz. This, combined with the fact that most vocals are miked too close can produce an aggressive and irritating result on a good playback system. A selective reduction of the region around 5 kHz is often effective in curing this.
Thus we see that frequency response adjustment during playback is completely legitimate and frequently necessary.
As to the argument that response-adjusting circuits are somehow "impure"…you can do anything badly or well. Poor circuit implementations are poor. Good ones are good. Really good ones are audibly transparent. It is possible to adjust frequency response without producing any audible collateral impairment. Given that, it would be stupid to deprive ourselves of a powerful tool. But like any tool, it must be designed correctly and used with skill and judgment.
- The "Right Thing", a proper tone control.
Traditional "Bass" and "Treble" controls have limited usefulness. The control is too coarse and the inflection frequencies are usually not in the right place.
Graphic equalizers are available which divide the spectrum up into several bands. Most of these products, even "pro" units have fairly poor performance. Even if the functionality is useful, the audio quality will be damaged.
Parametric equalizers are almost exclusively the domain of professional audio. Some have very good performance. The problem with using them for listening is that they are too flexible and difficult to use. By the time you have achieved the desired settings, you have to start the music over again.
The graphic and parametric equalizers are almost always single-channel units, so you need two for stereo. If they are dual units, you still have to adjust each channel separately. This is to be avoided not only because it is inconvenient. In stereo reproduction it is essential to preserve the identical response in both channels. Because phase and amplitude responses are linked, introducing dissimilar response in the two stereo channels will produce useless results.
Based on all of the foregoing discussion, here is a set of requirements for a truly useful tone control for playback purposes:
- Amplitude adjustment - boost or cut - is six frequency regions corresponding to important perceptual attributes. These are
|| deep bass
|| mid bass
|| 500 Hz
|| lower midrange
|| 2500 Hz
- Amplitude adjustment increments and range
Increments of 0.5 dB for small adjustments from 0.5 to 3.0 dB
Increments of 1.0 dB for middle adjustments from 4.0 to 6.0 dB
Increments of 2.0 dB for extreme adjustments from 8.0 to 10 dB
Total adjustment range of 10 dB boost or cut in each band
- All adjustments affect both channels identically to preserve stereo identity
- Bypass function so the adjustments can be easily compared with the unadjusted response
- All controls are stepped for exact repeatability of settings
- Absolute silence whether the filters are engaged or bypassed
- Minimum number of controls
- Simple - intuitive to use
View the NBS Universal Tone Control on our website www.nbscables.com
D. Michael Shields: firstname.lastname@example.org