Phase linear highpass filter Determines whether highpass filtering is done phase linear (with artifacts), or non-phase linear (without artifacts).
Phase linear means that the shape of the bass is not changed (except that low frequencies are removed). This causes some artifacts (chopper like sounds), especially at lower latency or quality settings.
Non-phase linear means that the shape of the bass is allowed to change. It will still sound the same, but the locations of peaks in the signal will move.
Possible settings:
Automatic selection
Phase linear at latencies 2048 and 4096 samples, non-phase linear at latencies 512 and 1024 samples.
Always phase linear
Never phase linear
An additional advantage of non-phase linear filtering is that it moves different bass frequencies around in time. This is not or hardly noticeable, but it does offer an advantage to the Advanced Clipper filter for short bass spikes: Because the bass is spread over time, Loudness can boost it further, resulting in louder bass levels without affecting the rest of the sound.
Highpass filter order (non-phase linear) The order of the highpass filter.
A higher value means steeper filtering. This can in some cases lead to unnatural sounding bass.
Post filter to avoid DC offset Extra filter later in the chain to remove any newly added DC offset.
Reduce post filter artifacts Filters the post filter output to remove some artifacts caused by filtering.
Lowpass panel Settings that control removal of high frequencies.
Lowpass frequency Remove high frequencies.
Controls the lowpass frequency. Tones above this frequency are removed.
This filter is very steep. The volume starts to drop a few hundred Hz below the configured frequency, and no frequencies above the set frequency should be coming through. The lowpass filter is always phase linear.
Some special values are:
15000 This is the lowpass frequency that should officially be used for FM stations. Since the filter is very steep, slightly higher frequencies should also work, and result in a better output quality.
4500 Hz
The lowpass frequency for AM stations in Europe.
Filter before processing (never below 16 kHz) Filters out some high frequencies to protect processing against audio problems.
Some tracks from around 2010-2013 have a high pitched tone in them, which causes compressors (not just in Stereo Tool but in nearly all audio processors) to go haywire. If this setting is enabled, such frequencies are filtered out before processing starts, which solves the problem.
