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virtual_equalizer.8
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virtual_equalizer.8
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.\"
.\" Copyright (c) 2019 Google LLC, written by Richard Kralovic <riso@google.com>
.\"
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"
.Dd March 13, 2019
.Dt VIRTUAL_EQUALIZER 8
.Os FreeBSD
.Sh NAME
.Nm virtual_equalizer
.Nd audio equalizer
.Sh SYNOPSIS
.Nm
.Op Fl h
.Op Fl o
.Op Fl q
.Op Fl d Ar devname
.Op Fl w Ar what
.Op Fl p Ar part
.Op Fl c Ar channels
.Op Fl f Ar file
.Sh DESCRIPTION
.Nm
sets the given frequency response for the given
.Xr virtual_oss 8
instance via the control character device given by the -d option.
The design goal of this equalizer is to provide precise equalization
for arbitrary requested frequency response at the expense of higher
latency, utilizing a so-called finite impulse response, FIR, filter.
.Pp
The requested frequency response is configured via standard input or
the file specified by the -f option.
There is one control point in per line.
Each line consists of two numbers, frequency in Hz and requested
amplification.
Amplification between two consecutive control points is a linear
interpolation of the given control point values.
.Pp
To make the filter finite, it is windowed in time domain using a Hann
window.
The windowing actually modifies the frequency response - the actual
response is a convolution of the requested response and spectrum of
the window.
This is, however, very close to the requested response.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl q
Be quiet and don't print anything to standard output.
.It Fl d Ar device
The
.Xr virtual_oss 8
control character device.
.It Fl w Ar what
Select what part the FIR filter should apply to.
Valid values are: rx_dev, tx_dev, rx_loop and tx_loop.
The default value is tx_dev.
.It Fl p Ar part
Select the index of the part given by the -w option to apply the filter to.
Default is zero.
.It Fl c Ar channels
Select number of channels to apply filter to, starting at channel zero.
By default all channels of the given part are updated.
.It Fl f Ar file
Read filter coefficients from the given file instead of standard input.
.It Fl o
Turn equalizer off.
.It Fl h
Show usage.
.El
.Sh EXAMPLES
To pass only frequencies between 200Hz and 400Hz:
.Bd -literal -offset indent
# Note that the -F and -G options enable FIR filtering.
virtual_oss -B -C 2 -c 2 -S -Q 0 -b 32 -r 48000 -s 8ms -F 80ms -G 80ms \\
-f /dev/dsp -d dsp.virtual -t vdsp.ctl
# For simplex operation use this:
virtual_oss -B -C 2 -c 2 -S -Q 0 -b 32 -r 48000 -s 8ms -F 80ms -G 80ms \\
-R /dev/null -O /dev/dsp -d dsp.virtual -t vdsp.ctl
# Load normalized filter points to avoid sample value overflow
cat << EOF | virtual_equalizer -d /dev/vdsp.ctl -w tx_dev -p 0 -c 2
NORMALIZE
199 0.0
200 1.0
400 1.0
401 0.0
EOF
# Load FIR filter based on sine frequency points
cat << EOF | virtual_equalizer -d /dev/vdsp.ctl -w tx_dev -p 0 -c 2
199 0.0
200 1.0
400 1.0
401 0.0
EOF
.Ed
.Pp
.Sh FILES
.Sh SEE ALSO
.Xr virtual_oss 8
.Sh AUTHORS
.Nm
was written by
.An Richard Kralovic riso@google.com .
.Pp