How to control equalizer within command line?

The pulseaudio equalizer is reading his settings in the user file ~/.config/pulse/equalizerrc

To display it: 

cat ~/.config/pulse/equalizerrc

So, as example, to give a value of 10DB on the 5th band of the eq, and directly ear the change:

sed -i '19s/.*/10.0/' ~/.config/pulse/equalizerrc | pulseaudio-equalizer toggle

To explain furthermore, sed will replace all line numbered 19, and will replace it by 10.0 on the config file, then the equalizer is restarted/toggled to get the result.


Here's a script, adapteded from qpaeq that comes with Pulseaudio:

#!/usr/bin/env python
# pulse-set-eq
import os,math,sys
import dbus

# Source adapted from utils/qpaeq of PulseAudio

def connect(): # copied from qpaeq
    try:
        if 'PULSE_DBUS_SERVER' in os.environ:
            address = os.environ['PULSE_DBUS_SERVER']
        else:
            bus = dbus.SessionBus() # Should be UserBus, but D-Bus doesn't implement that yet.
            server_lookup = bus.get_object('org.PulseAudio1', '/org/pulseaudio/server_lookup1')
            address = server_lookup.Get('org.PulseAudio.ServerLookup1', 'Address', dbus_interface='org.freedesktop.DBus.Properties')
        return dbus.connection.Connection(address)
    except Exception as e:
        sys.stderr.write('There was an error connecting to pulseaudio, '
                         'please make sure you have the pulseaudio dbus '
                         'module loaded, exiting...\n')
        sys.exit(-1)

def get_sink(str):
    connection=connect()
    path='/org/pulseaudio/core1/sink%s'%str
    sink=connection.get_object(object_path=path)
    return sink

args = sys.argv[1:]

sinknum = args.pop(0);
sink = get_sink(sinknum);

prop_iface='org.freedesktop.DBus.Properties'
eq_iface='org.PulseAudio.Ext.Equalizing1.Equalizer'
sink_props=dbus.Interface(sink,dbus_interface=prop_iface)

def get_eq_attr(attr):
    return sink_props.Get(eq_iface,attr)

sample_rate=get_eq_attr('SampleRate')
filter_rate=get_eq_attr('FilterSampleRate')
nchannels=get_eq_attr('NChannels')

sys.stderr.write('channels %d, sample rate: %f, filter sample rate: %f\n'%
    (nchannels, sample_rate, filter_rate))

channel = int(args.pop(0));
preamp = float(args.pop(0));

freqs = [];
coeffs = [];
while len(args) > 0:
    if len(args)==1:
        sys.stderr.write('Odd number of frequency/amplification arguments (%d)\n'%(len(freqs)*2+1))
        sys.exit(-1)
    sys.stderr.write('(%s, %s)\n'%(args[0],args[1]))
    freqs.append(float(args.pop(0)))
    coeffs.append(float(args.pop(0)))

#sys.stderr.write("freqs: "+str(freqs)+'\n');

freqs = list([int(round(x*filter_rate/sample_rate)) for x in freqs])
#sys.stderr.write("translated freqs: "+str(freqs)+'\n');

freqs = [0]+freqs+[filter_rate//2];
coeffs = [coeffs[0]]+coeffs+[coeffs[-1]];
#sys.stderr.write("proper freqs: "+str(freqs)+'\n');

# for some reason this fixes the types of the arguments to SeedFilter
sink=dbus.Interface(sink,dbus_interface=eq_iface)

# set the filter coefficients
sink.SeedFilter(channel,freqs,coeffs,preamp)

First you want to load the equalizer module as well as the DBus protocol module:

pactl load-module module-dbus-protocol
pactl load-module module-equalizer-sink sink_name=... sink_master=...
pactl set-default-sink ...

Then make some noise, or music or whatever:

play -n synth pinknoise gain -10

Then call the script with the sink number, the channel index you want the equalizer to apply to, a preamp (scaling) factor, and a list of (frequency, coefficient) pairs. The frequency list doesn't have to be dense, since it is interpolated (see seed_filter in pulseaudio/src/modules/module-equalizer-sink.c) to get the filter coefficients. If you specify the total number of channels as the channel index then the update applies to all channels. Use pacmd list-sinks to get the sink number.

For example, if the sink number is $SINKNUM and it has 2 channels, then this resets the equalizer to all 1's, as you can verify by opening qpaeq:

./pulse-set-eq $SINKNUM 2 1.0    100 1.0

Here 100 Hz is arbitrary; the list needs to be not empty and can't start with zero. The frequencies must be between 0 and 32768 (the maximum for me, not sure if it is configurable, see the filter_rate variable above - this is half that). The script uses the amplification coefficients of the smallest and largest frequencies specified on the command line, for the frequencies below and above these, respectively, so in this case the whole spectrum will be assigned an amplification rate of 1.0. At this setting, the equalizer will leave the signal unchanged (in theory at least).

Be careful not to damage your speakers, but for example you can play around by creating pink noise and setting the equalizer to a spike (at 100x amplification) at a single frequency (500Hz):

./pulse-set-eq $SINKNUM 2 1.0    499 0 500 100 501 0

When I do this, I can hear a discrete succession of tones of different random volumes, all at 500Hz, which I presume are belonging to successive DFT windows in the implementation of the filter. It is somewhat pleasant. Playing music through this filter is amusing. Such a sharp "bandpass" would not be possible using a normal graphical equalizer with no command-line version.

The following example makes a filter that goes up and down in frequency, a bit like a siren. Obviously you have to have some music playing or noise or something to hear the effect.

SINKNUM=12; NCHAN=2;
while true; do
    for i in $(seq 500 10 1500) $(seq 1500 -10 500); do
        ./pulse-set-eq $SINKNUM $NCHAN 1 \
            0 1 $(( $i - 300 )) 1 \
            $i 5 $(( $i + 300 )) 1 \
            32768 1;
    done;
done

Tags:

Pulseaudio

Recent Posts