About This Application Note
The PlayBasic Reusable Subsystem Application Note contains a brief description and tuning instructions for DSP Concepts’ PlayBasic basic audio playback processing Reusable Subsystem.
PlayBasic – Basic Audio Playback Processing Reusable Subsystem
PlayBasic is DSP Concepts’ proprietary basic audio playback processing algorithm. It is available as a Reusable Subsystem in AWE Designer.
PlayBasic consists of five cascaded biquad filters for equalization and a three-band dynamic range compressor. PlayBasic includes gain control between the biquad filters and the three-band compressor. The three-band compressor is followed by a full-band compressor and a soft clipper to minimize any clipping distortions. PlayBasic works for mono or stereo audio streams and with all sampling rates and block sizes. It is effective for various audio playback hardware devices such as loudspeakers, headphones, earbuds, and smart phones.
Figure 1 shows the block diagram of PlayBasic’s internal processing. The components in blue blocks are tunable.
Figure 2 shows an example layout demonstrating the PlayBasic Reusable Subsystem. This example layout is designed to run in Native Mode with a file input; audio signals must be assigned to appropriate channels for running the layout on a target device.
The PlayBasic Reusable Subsystem includes an inspector which allows users to tune the equalization filters, the main volume, and the compressors. Figure 3 show the inspector panel of the PlayBasic Reusable Subsystem.
The Main Volume is applied after the equalization filters and before the compressors. High Main Volume gains may be counteracted by the compressors depending on the compressors’ tunings.
Users can design equalization with five cascaded biquad filters.
There are 22 filter types available (Table 1). Depending on the selected filter types, users can tune a cutoff frequency, a Q value, and a filter gain for the filter. If a biquad stage is unused, select the Bypass option for that filter.
Butterworth 1st-order LPF
Butterworth 2nd-order LPF
Butterworth 1st-order HPF
Butterworth 2nd-order HPF
1st order APF
2nd order APF
Bessel 1st order LPF
Bessel 1st order HPF
Self Low 1st order Asym
Self High 1st order Asym
Self Low 1st order Sym
Self Low 1st order Sym
Table 1: Filter type options for equalization filter
Dynamic Range Compressors
As shown in Figure 1, there are four tunable dynamic range compressors. Each compressor has the following tuning parameters.
Threshold (dBFS) – The compressor attenuates signals above this level.
Gain (dB) – The constant gain in dB applied to the compressor output.
Ratio – The input and output level ratio. Higher ratio values cause the compressor to attenuate signals above the threshold more aggressively.
Knee depth (dB) – Larger knee depth values provide smoother gain transitions around the threshold.
Attack time (ms) – The envelope detector attack time for estimating the signal level.
Decay time (ms) – The envelope detector decay time for estimating the signal level.