Dynamic Range Audio [Expert Explained]
Dynamic range (DR) audio is a difference between maximum and minimum signal levels in the first approach. But it's not that simple. Read explanation methods of measurement, its difference by audio software developer Yuri Korzunov.
Introduction
Dynamic range may have 2 meanings: for audio device / software / format and audio signal.
- DR of audio device is the difference between maximal and minimal allowable levels of signal inside the device / software / format.
- DR of an audio signal is the difference between maximum and minimum signal levels.
In this article, we will discuss first meaning.
The dynamic range has multiple definitions. Because minimum and maximum levels may be measured in various ways.
Read details about minimum and maximum level issues.
How dynamic range calculated
When a signal pass through audio unit/software (as digital as analog) its level is limited by minimal and maximal values. Dynamic range is calculated as difference between these levels:
DR = [Maximal Level, dB] -[Minimum Level, dB]
Maximum level
Maximum level of an audio signal
When signal achieves overload value, it gets non-linear distortions, that is shown at the left part of the picture as red components.
Overload audio. It is output signal for input sine
Pure digital systems (as example, software) have a sharp border between distorted and non-distorted signals.
Example:
16 bit signal has maximal value: 215-1.
When signal achieves the next level (215), it causes overload (mathematical overflow) and 215 is transformed to -215 (minimum allowable value).
Digital signal overload
Such transformation can cause a loud click. To avoid the click, a processing is performed in higher bit resolution. Before conversion to target (lower) bit resolution, a signal is checked to overload. If there is overload, overloaded samples level is limited bay maximal allowable one. Such overload kind is the same as traditional analog, that causes distortions without big "digital overload clicks".
Analog overload has smooth overload border. At the upper right part of the picture input-output level characteristic is displayed.
Analog non-linear distortions. Input-output characteristic
When input signal level approaches to maximal limit, distortions grow too. Because the distortion intensity depends on level due to non-linearity.
That characteristic may be linear (simple line) or non-linear, like one, displayed at the picture.
Let's look to the highest levels. A-area at the characteristic impact to waveform in area B of the output signal. So non-linearity kind in the A-area defines distortions at the output (B-area) when input signal level about maximal value. In other words, different levels of input signal generate various levels of distortion components at the output.
For digital signal simple binary logic ("with" or "without" distortion) may be applied.
For analog signal we can estimate various distortion levels for different input signal levels. There is a smooth overload border.
Therefore for analog signal, the maximal level may be accepted as a level that causes target distortion intensity.
Read more: Digital vs Analog audio...
As example, as maximal level may be accepted level where the share of distortions in total energy more, than the target value.
Minimum level
When a signal level is decreased, it achieves noise floor and hide under it. It is fairly for both digital and analog signals.
Minimal level of audio signal
There is difference in noise nature. Analog noise is a noise of electronic components. Pure digital noise is quantization noise. Captured digital signals have both kinds of noise: by electronic components and quantization. But it does not matter for minimal level estimation.
Therefore, minimum level has a different sound quality for its different values.
For pure digital units and software, quality is defined by signal/noise ratio.
For analog systems, quality is also defined by the non-linearity of the input-output characteristic of measured device.
When we consider dynamic range as the difference between a noise floor and overload level, quality estimation is lost.
When signal "drowns" in noise we can't recognize it. So such way of dynamic range estimation is too optimistic.
We want to listen minimum level in given quality. The quality is defined by signal/noise ratio.
Analog systems have different linearity for different levels. The non-linearity generates distortions: spectral products, that correlate with an original pure signal. So we must account the distortions as noise too. We can look to similar example with highest levels here.
Signal/noise ratio
Signal/noise ratio is a ratio between energies of signal and noise.
Energy may be estimated as a square of a power spectrum.
Power is level2.
Signal/noise ratio at the power spectrum
If we can localize signal spectrum, rest spectrum we can accept as noise and distortions.
It is a reason why we can't use music as a test signal. Music have dense spectrum and it is almost impossible to separate noise, distortions and an original signal.
Also, using complex signals (multi-tones, as example) can cause issues of signal and noise separation.
We can step-by-step reduce the noise level to achieve given signal/[noise and distortions] ratio. This level is accepted as minimum.
Signal energy (square) calculation does not matter. But band of the signal may be accepted differently for different methods.
Also, noise and signal energies may be calculated accounting psychoacoustics: equal-loudness contour.
Frequently asked questions
What is dynamic range in audio? What is dynamic range sound?
Dynamic range is a property of an audio device or audio processing. Also, a music-recording-level range is considered as dynamic range. Read details...
What is a good dynamic range?
As measurement kind, the dynamic range may have different interpretations, that is bound with psychoacoustics.
Also, dynamic range depends on music genre.
Approximately, we can consider the minimum allowable signal/noise ratio of lowest signal like to analog devices - about 40...60 dB. It is the quietest place of a musical piece.
So, to found the difference between maximal loudness and noise floor, we should add to the difference between the quietest place and maximal loudness of the piece to the SNR.
Examples:
- When the difference between fortissimo and pianissimo (maximum and minimum loudness) is 60 dB: dynamic range is 60 dB and difference between maximum loudness and noise floor is 60 dB + [40...60] dB = 100 ... 120 dB.
- When the difference between fortissimo and pianissimo (maximum and minimum loudness) is 80 dB: the dynamic range is 80 dB and the difference between maximum loudness and the noise floor is 80 dB + [40...60] dB = 120 ... 140 dB.
What does dynamic sound mean?
It is sound with loud (or too loud) and quiet (to quiet) places.
Conclusions
- Simplified dynamic range is a difference between signal that causes overload and noise floor.
- Estimation of audio dynamic range should take into account sound quality.
- Dynamic range by goal #2 has lesser value than simplified definition by goal #1.
Simplified dynamic range estimation
Dynamic range estimation, taking into account sound quality
References
February 12, 2021 updated | since November 20, 2017