WAVES X-Hum Software Audio Processor User Guide
- June 10, 2024
- WAVES
Table of Contents
WAVES X-Hum Software Audio Processor
User Guide
The Noise Reduction Technology
licensed from Algorithmix ® GmbH, Germany.
All rights reserved.
Introduction
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Waves X-Hum reduces rumble, DC-offset, and hum while preserving excellent
audio quality. X-Hum is part of the Waves Restoration bundle, which restores
vinyl records and damaged recordings. X-Hum and the other Restoration plug-
ins have a friendly interface that is easy to learn and use.
This user guide describes:
- the problems X-Hum solves;
- how to use the software;
- the software user interface.
WHAT PROBLEMS DOES X-HUM FIX?
X-Hum effectively reduces all three of these problems:
-
Hum disturbance is usually caused by problematic ground-loop circuits.
Steady, low-frequency oscillation may occur in the recording, usually at a sub frequency of the AC used in that country. For example, Europe uses 240 VAC so an ungrounded loop can cause a 60 Hz hum. The fundamental disturbance can also cause harmonics at high enough amplitudes to create additional problems. -
Low-frequency rumble is caused by mechanical analog systems, such as
turntables and tape machines; it is not steady in pitch. -
DC offset tilts in the audio waveform to one side of the zero baseline.
HOW DOES X-HUM WORK?
Hum, rumble, and DC-offset disturbances are usually stable throughout the
afflicted recording. For this reason, an EQ device is better suited for
reducing the problem than a dynamic process. X-Hum uses higher order filters
with extremely narrow cut notches than those found in a typical EQ. X-Hum’s
notches can cut up to 60 dB at very narrow bandwidths.
Using X-Hum
X- Hum is divided into two sections:
- A high-pass filter eliminates rumble and DC-offset.
- Eight notch filters linked in a harmonic frequency structure eliminate steady-pitched hum.
Two parameters affect the high-pass filter:
-
Slope can be set to –12 or –24 dB/octave.
-
Frequency determines the filter cutoff frequency. Use a low cutoff frequency (i.e., 10 Hz) to eliminate DC offset and preserve the signal’s musically significant low- frequency content. Use a higher cutoff (i.e., 40– 80 Hz) to eliminate rumble.
The Harmonic Notch Filters section removes steady-pitched hum with different harmonic structures built above the fundamental oscillation. There are three parameters: -
The Frequency control sets the fundamental center frequency of the filter.
-
The Global Q sets the width of the notch filters. For very steady-pitched hum, use a narrow Q. If the hum’s frequency shifts throughout the recording, use a wider Q.
-
The Cut Gain of the notch filter can be set separately for each harmonic filter.
Three link modes allow different methods of altering the gain of the filters:
- Linked: All filters are linked such that altering one filter adjusts all filters at once while preserving their relative offsets.
- Odd/Even: Links the gain of filters 1,3,5,7, and 2,4,6,8 while preserving the relative offsets within the odd and even groups.
- Unlinked: Filters are not linked; all filters can be adjusted independently.
NOTE: Relative offsets are preserved until a maximum or minimum value is
reached. Once a filter has reached its limit, further movement of the other
filters requires unlinking.
Although some phase distortion occurs in most digital and all analog EQs,
these devices do not use the extreme slopes and cuts found in X-Hum. Since
phase distortion increases with these more extreme settings, we recommend
using X- Hum as moderately as possible to satisfy your requirements.
In many cases, a factory preset will solve your recording’s problems. If a factory preset is not suitable, find the preset that works best and alter its parameters to match the specific task.
X-Hum Controls and Displays
CONTROLS
High-Pass
ON/OFF SWITCH:
Turns the High-Pass filter on or off.
Default = Off
SLOPE:
Determines the order of the filter.
Settings: Moderate (12 dB/octave), Steep (24 dB/octave); Default =
Moderate
FREQUENCY:
Sets the High-Pass filter’s cutoff frequency.
Settings: 4–100 Hz; Default = 20 Hz
Harmonic Notch Filters
FREQUENCY:
Sets the fundamental frequency of the first filter for hum removal. The
subsequent seven filters are set harmonically relative to this filter. For
example a fundamental at 60 Hz would have its harmonics at:
602=120 Hz, 603=180 Hz, 604=240 Hz, 605=300 Hz, 606=360 Hz, 607=420 Hz.
Settings: 20–500 Hz; Default = 60 Hz
Q:
Sets the bandwidth of the notch filter. These notch filters are capable of
very narrow Qs. Higher numbers correspond to a narrower Q.
GAIN:
X-Hum has separate gains for each of the eight harmonic notch filters. Since
these are cut filters, gains are negative so the absolute value is shown. The
gains can be altered from the graph by clicking and dragging a notch’s +
marker.
The Gain behavior resulting from dragging follows the Link mode setting (see
below).
Settings: 0–60 dB; Default = 0
LINK MODE:
The Link mode selector has three settings that define how altering one
filter’s gain affects the others:
Linked: All filters are linked such that altering one filter adjusts all
filters at once while preserving their relative offsets.
Odd/Even: Links the gain of filters 1,3,5,7, and 2,4,6,8 while preserving the
relative offsets of odd and even groups.
Unlinked: Filters are not linked; all filters can be adjusted independently.
Offsets are preserved in linked mode only when gain adjustments yield settings
within maximum and minimum boundaries.
MONITOR
The Monitor control toggles between Audio and Inverse.
- The Audio path plays the processed audio; this is the normal mode to monitor X-Hum’s effect.
- Inverse mode keeps the filters in the same position but boosts (instead of cuts) while applying appropriate gain reduction. This technique is well known to sound engineers as they search for a problematic feedback or resonant frequency while equalizing a concert environment. It is sometimes easier to spot the problem by boosting suspect frequencies to exacerbate the problem than by cutting to solve it directly. The Inverse function does not yield a boost filter shape that is perfectly symmetric to the cut filter’s. The boost filters are not as narrow and never boost 60 dB.
The High-Pass filter is not included in Inverse mode and is turned off.
The following figure shows the X-Hum graph in Inverse mode:
DISPLAYS
X-HUM GRAPH
The graph represents the X-Hum notch filter settings. The x-axis shows frequencies in the range 10 Hz – 4 kHz (logarithmic scale). The y-axis shows amplitude from +6 dB to –60 dB.
OUTPUT METERS AND CLIP LIGHTS
The output meters show the output level in dBFS (dB below Full-Scale digital).
The clip light above the meters lights when the output exceeds 0 dBFS.
You might be wondering: How can a cut-only device produce clipping? Since X-
Hum’s EQ filters are not phase linear, they introduce some phase distortion of
the input signal. This is common in all non-phase-linear EQs. Due to the
shifting phase of some frequencies in relation to others, parts of the signal
that were close to the full scale may suddenly exceed it. It is important to
know when this occurs so clipping is not mistaken for other noise. To
eliminate clipping reduce the gain of the input signal.
WaveSystem Toolbar
Use the bar at the top of the plugin to save and load presets, compare
settings, undo and redo steps, and resize the plugin. To learn more, click the
icon at the upper-right corner of the window and open the WaveSystem Guide.
References
Read User Manual Online (PDF format)
Read User Manual Online (PDF format) >>