Dynamic range. 2003/08

While dynamic range is one of the most important aspects of recorded music, it is also one of the least understood and most often abused areas of the recording and playback chain. Simply put, the dynamic range of a sound refers to the extremes between the loudest and the softest sounds. A visual example is that of the dynamic range of a grayscale spectrum: white at one end and absolute black at the other. For a greater discussion of this and other definitions, please read "Sonics" from 08/01.
 Absolute dynamic range can be affected by the noise floor of any given situation (the room you listen in, the room the instrument was recorded in, internal noise of any equipment, etc.). The higher the noise floor, then lower relative dynamic range is available. The noise floor establishes the lowest usable signal level for a given situation. For the sake of further discussion, let me digress to offer a simple view of a level meter. Digital recording meters operate from left to right with the loudest possible sound indicated on the far right by 0dB. Moving from right to left are indications of how many dB below 0dB the signal level is. These numbers are preceded by a "-" since they are below the absolute 0dB of maximum level. A mastering-type meter might start at -100dB on the far left up to 0dB on the far right. A standard compact disc is capable of a dynamic range of 96dB. That is, the difference between the loudest and softest sounds can be as far apart as 96dB. For reference, really good analog reel to reel is capable of a dynamic range in the high 60's. The very best virgin vinyl recordings could (for at least a single play) achieve 60dB, while the bulk of vinyl averaged around the low 50's. On our digital meter this means that, if the loudest portion reaches 0dB, the lowest signal will have to be at -96dB.  

Here is where noise floor enters the picture. Since the noise floor of all but the absolute quietest spaces is well over -96dB, the practical dynamic range of any recording is already limited by the source of the sound. If you have a room with a noise floor that is at -65dB, you can not record any sounds below that level as they will be lost in the noise of the room. This is one reason why recording spaces strive for great acoustic isolation of outside influences. The higher the noise floor, the lower the overall dynamic resolution of the room, and, as we will see, the greater the harm to the integrity of the sound created by the instrument. Here is a discussion of dynamic range from Sound Studio by Dennis Nardantonio:

"There are basically two characteristics that determine what something sounds like: the dynamic profile called the envelope and the harmonic content. ... The envelope is not the only signature of sound. The harmonic content is the other aspect. Consider the simplest sound waveform. It can be described as a trigonometric function called a sine wave. A plucked string vibrates the air as the string oscillates back and forth. This oscillating movement is sinusoidal, and its displacement can be described graphically as displacement versus time. ... This is a simple case of one fundamental sinusoidal tone, but actually sounds are much more complex than that. Sounds are composed of a multiplicity of sinusoids called harmonics. ... A violin has about five significant harmonics in addition to the fundamental... . Harmonics are also called overtones. It is these overtones that allow recognition of sound." 

Simply stated, messing with the dynamics inalterably changes the fundamental sound of any given instrument. So why mess with dynamics? Environmental noise of the playback system, inherent noise in the playback system, limitations of the recording medium, limitations of the microphones, and sometimes even limitations of the mixing console all contribute to the use of compression. When the recording medium was not capable of capturing a dynamic range greater than about 65dB and the playback mediums could store even less range, it was important to limit the dynamic range so that 1) the quietest portions did not get lost in the noise floor of the two mediums and 2) so that raising the level of the recording to get the sounds above the noise floor did not push the loudest sections over the maximum signal level that could be captured or played back.  

Cassette tape was a good example of this noise floor. If you attempted to record very soft passages with cassette, you often found the finer points of the sound lost in the tape hiss (noise floor). Noise reduction was created as a way to "push" the noise floor down even further in order to capture more dynamic range. Compressors can either raise the lowest sounds up, reduce the loudest sounds down, or some of both to "compress" the initial dynamic range. As you compress the dynamic range you also increase the average level of the sound. The higher the average level, the higher the overall perceived level of the sound becomes. It is important to understand this perception as compression does not allow for any louder recording than the maximum level dictated by the recording or playback format as would be achievable without compression. In the digital world, 0dB is 0dB and nothing louder can be captured.

For many years, playback gear had reduced dynamic capability compared to that of the professional gear used to record the music to begin with. The advent of digital recording and the compact disc all at once not only raised the bar on dynamic range an astounding amount, but it also leveled the playing field. For the first time ever the music-listening consumer could have access to the "master tapeÓ so to speak. No longer was it necessary for the recording to go through the damaging effects of compression in order to make the music usable on the lesser playback systems. However, this new format only addressed one portion of this problem. The noise floor of the listening spaces did not change. Suddenly, noise floors that were not impacting the dynamic range too much became a bigger problem. The simultaneous explosion of music listening in locations other than living or dedicated listening rooms, and the beginning of the loudness wars had a devastating impact on our newfound dynamic freedom. Listening to music in the car has eclipsed listening to music in the home and the noise floor of even the quietest cars far exceeds that of a reasonably quiet listening room. If you do not want the quieter passages lost in the rumble of the road, you reach for the compressor. Due to all the environmental noise, it has become commonplace for studios to reduce the dynamic range even further in order to "cut through" other noise. With the mantra that "louder is better" and a lack of patience to sit and listen critically, the subtlety of unconstrained dynamics is lost.  

A common observation made about wide dynamic range recordings is that they are "low" sounding when, in reality, their loudest parts are as loud as anything recorded on CD. The difference is that that loudness is not all the same all the time. Suddenly you have a volume pallet from which to listen. Because the range has not been artificially reduced, it becomes necessary to actually use the volume control to turn up the level to the appropriate point that puts the whole dynamic spectrum in focus. Once set for the loudest parts, the quieter parts will all fall into place.

It does not help that poorly educated or informed music writers perpetuate this misunderstanding. A review in an audiophile publication of the soundtrack from Titanic noted that it would have been nice if the volume level of the music did not keep changing so much, which required the writer to continually adjust the volume. Thankfully such a complete misunderstanding of the role of dynamics in orchestral music was at least given the opportunity of rebuttal by the engineer and record label. The ironic outcome is that, while the dynamic capability of our recording and playback medium is at an all time high, the dynamic range achieved is now at an all time low. It is not uncommon for me to find CDs that have a dynamic range of less than 5dB. I have measured one that was actually less than 3dB! 10-15dB seems fairly normal these days, a far cry from the capabilities of even the 78 rpm record. Music compressed this far has a complete lack of "air" and "space", there is no breathing room for the notes to develop, and the overall presentation is "in your face all the time. This may be good for the car, but it is downright horrible sounding when heard in a good listening environment. Compressed dynamics contributes greatly to listener fatigue, further decreasing our desire to sit and give a performance our undivided attention.

Compression has gotten so bad that the engineering community is becoming even more vocal about the destruction of music through compression. The introduction of SACD and DVD-Audio with their further increase in dynamic range is pushing this issue to the front. Very few recordings make use of the current dynamic capability of the CD. Is there really a need for another 30dB of dynamic range? We are certainly not being held back by the current format and selling a new format based on increased dynamic range seems like a good marketing idea, but one which little practical use may be made. One hope is that the new format gives some the "excuseÓ they need to bring back some dynamic range. Of course, this will incense consumers who will once again have to consider buying yet another version of some piece of music, now with "new improved dynamic range!Ó Such is the problem of playing your audience cheap to begin with. As SACD and DVD-Audio move forward, re-engineers are surprised to find out that the vinyl issues of the music they are working on contain greater dynamic range than the CD versions and are scrambling for the originals in order to get the dynamics back. Newer recordings in these formats seem to be making an attempt to start again with a renewed sensitivity to the music. For these reasons it is not clear that all SACDs and DVD-Audio discs are inherently better than their CD counterparts. They certainly can be, but often the better "soundÓ is simply a result of greater care going into making the masters to begin with, a care and a capability that has been available, but under utilized, since the advent of the standard compact disc.

Compressed recordings can not be effectively uncompressed, but uncompressed recordings can be easily compressed during playback. Perhaps the market needs to push the many low cost compressors on the market to deal with this issue. With large scale circuit integration, this function could take the place of the mis-named loudness button that used to populate almost all low and mid-fi electronic gear. Let each listener choose without forcing all listeners to adopt a single point of view.

© Cadence Magazine 2003

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