What is maximizer and why
Maximizer (digital peak limiter) is a dynamic processing device that increases the level of the audio signal during mastering. Sometimes other types of devices are called maximizers, for example, psychoacoustic processing such as BBE Sonic Maximizer – we will not consider them here. We will get acquainted with the principles of operation of dynamic processing devices and compare with each other some popular models of software maximizers.
Volume and levels
The sound volume depends not only on the sound level (or sound pressure), but also on its spectral-temporal composition. If the frequency balance of the phonogram is already determined and it is undesirable to change it, then to increase the volume of the phonogram it is necessary to increase the signal level. Why increase the volume? There are two reasons for this. The first of these is that loud music more often seems “prettier” than quiet, and attracts more attention. Therefore, most producers do their best to increase the level of phonograms during mastering: after all, its commercial success may depend on this. The second reason for increasing the volume is the desire to make full use of the dynamic range of the audio recording medium, whether it be a CD or an analog tape. It is also important to make maximum use of the dynamic range of the playback device so that the recording does not sink in noise.
When recording sound, carriers usually limit the peak level of the signal to the overload, rather than its rms power (this is a somewhat simplified, but close to reality model for most analog and digital sound carriers). The ratio of the peak level of the phonogram to its root mean square level (RMS) is called the peak factor (crest-factor, cross-factor). A square wave (meander) has a single peak factor of 0 dB. The peak factor of the sine wave is 3 dB. Phonograms with wide dynamics or sharp peaks have a high peak factor (20 dB or more), and highly compressed phonograms have a low peak factor (10 … 15 dB). It is clear that with limited peak power, a phonogram with a lower peak factor can achieve a higher volume. In order to reduce the phonogram peak factor, it is passed through dynamic processing devices (Fig. 1). Consider their principles of work.
What is maximizer and why (Maximizers)
Fig. 1. Phonogram before and after dynamic processing. Decrease in peak factor. There is no clipping here, and the sound is perfectly acceptable for the radio
Dynamic processing devices
The main devices for working with phonogram levels are dynamic processing devices. The principle of operation of these devices is to analyze the level of the audio signal entering them and change this level according to some law. The main parameters of the dynamic processing devices are the transfer characteristic and the attack / recovery time.
The transfer characteristic (not to be confused with the amplitude-frequency characteristic) is the dependence of the desired output sound level on the input level. In accordance with the transfer characteristic, the dynamic processing device determines the gain that must be applied to the input signal at each moment of time. An example of the transfer characteristic is shown in Fig. 2. Such a dynamic processing device is called a compressor; it transmits sounds with an amplitude up to -20 dB without changing and reduces the amplitude of all sounds above -20 dB. Thus, the compressor makes loud sounds quieter, narrowing the dynamic range of the phonogram.
What is maximizer and why (Maximizers)
Fig. 2. The transfer characteristic of the compressor. The threshold is -20 dB, compression ratio 2: 1
The fracture in the transfer characteristic is called the knee point. The input level corresponding to the knee is called a threshold. The angle of inclination of the transfer characteristic above the threshold determines the compression ratio (ratio, compression ratio). A compression ratio of 2: 1 means that when the input level is increased 2 dB above the threshold, the output level will increase by only 1 dB. If the compression ratio is equal to one, then the sound level when passing through the device will not change. If it tends to infinity, then the device will limit the amplitude of the output sound to a threshold value. Such devices are called limiters; they limit the dynamic range. If the compression ratio is less than unity, for example 1: 1.5, then this means that when the input level exceeds the threshold, the device will increase the output level compared to the input level. Such devices are called expanders, they expand the dynamic range. There are other types of dynamic processing devices: gates, dacers, levellers, etc., with their specific transfer characteristics and operating parameters.
Sometimes the transfer characteristic is smoothed so that there are no sharp corners (Fig. 3). This mode is called soft knee or soft threshold. A compressor with a soft threshold begins to slightly decrease the signal level even before it reaches a threshold value.