Dynamic Range? What and why

The audio output of some android phones is now better than CD quality, but you need suitable software, such as HeadP on Android 5 or greater, to actually use this capability.

But is better dynamic range helpful?  Chris [c] says no – but he is talking about source media and not about playback that has the same difficulties as recording and production, for which his answer is yes!  So what sort of playback needs better dynamic range?

I will attempt to explain without being irritatingly arcane.

1.      Here, dynamic range is the loudest measured by quietest sound that can be produced.
It is loudest relative to quietest; a ratio of loudest to quietest.

2.      There are many measures of loudness. One can measure amplitude gain or peak power, or time-averages of power, for example.

3.      Here I will use peak power in decibels to measure relative loudness.

4.      Then, a sound is 10 decibels louder if it has 10 times more power.

5.      And a sound is 20 decibels louder if it has 100 times more power.

6.      Human hearing can have a dynamic range of up to 130 decibels [b]:   That is a lot!!!!

7.      CD-quality, 16-bit audio has a dynamic range of about 90 decibels in practice [a].

From 6 and 7 you might conclude that CD-quality is good enough [c].  But if playback involves processes similar to recording and production, there are problems:

1.      Any processing, like adding echoes, may require “headroom” to avoid clipping the signal.
This is because the loudest peak is not known in advance. Then maybe only 70 decibels of dynamic range remains. After further processing, maybe only 60 decibels remains.

2.      Then a quiet section will either be too quiet, or too noisy if the volume is increased, because only a few bits remain to encode the sound.

A 32-bit floating point representation of the signal solves the software part of this problem. There remains only the question of whether the output hardware (digital-to-analogue converter and amplifier) on particular phones is adequate. These are changing fast, so any comment here would soon be out of date. Look for a brand that cares about audio.

References

1. Fries, Bruce; Marty Fries (2005). Digital Audio Essentials. O'Reilly Media. p. 147. ISBN 0-596-00856-2.
2. Sensitivity of Human Ear  http://hyperphysics.phy-astr.gsu.edu/hbase/sound/earsens.html#c2
3. Montgomery, Chris (March 25, 2012). 24/192 Music Downloads ...and why they make no sense