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Re: [SoX-users] synth seems to generate "pops"?
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From: Brian W. <bri...@gm...> - 2025-03-25 16:53:26
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On Tue, 25 Mar 2025 at 12:56, Jan Stary <ha...@st...> wrote:
> On Mar 25 11:58:15, bri...@gm... wrote:
> > I'm thinking of using sox's synth capability to make myself a simple
> > hearing tester. It will play a bunch of tones at various frequencies,
> > channels and volumes and record my response, or not.
>
> What version of SoX is it?
>
bwatson@puck:~$ sox --version
sox: SoX v14.4.2
bwatson@puck:~$ dpkg -l | grep alsa
ii alsa-base 1.0.25+dfsg-0ubuntu7
all ALSA driver configuration files
ii alsa-topology-conf 1.2.5.1-2
all ALSA topology configuration files
ii alsa-ucm-conf 1.2.6.3-1ubuntu1.12
all ALSA Use Case Manager configuration files
ii alsa-utils 1.2.6-1ubuntu1
amd64 Utilities for configuring and using ALSA
ii libsox-fmt-alsa:amd64
14.4.2+git20190427-2+deb11u2ubuntu0.22.04.1 amd64 SoX alsa format
I/O library
bwatson@puck:~$ uname -a
Linux puck 5.15.0-134-generic #145-Ubuntu SMP Wed Feb 12 20:08:39 UTC 2025
x86_64 x86_64 x86_64 GNU/Linux
> After a bit of reading I have figured that something like this:
> > play -r 44100 -n -t alsa synth 0.5 sin 5000 vol -25dB remix 1 0
> > wrapped into a script with the frequency, gain and remix parameters
> > replaced with variables will work exactly as I had hoped.
>
> Why do you need the 44100 sample rate?
>
Just because it was the sample rate in the example that I learned this
syntax from.
> Why are you only using half a second of sound?
>
Because I want to generate lots (probably hundreds) of tones one after the
other and see if I hear them or not. Half a second seems long enough that
I should be able to hear it, but not long enough that I waste time
listening once it has been heard.
>
> > Except - when I listen to the generated sounds there is a small pop, or
> > crack, at the start and end of each sound.
>
> I suspect being off the zero crossings:
> Half a second of a 5 kHz sine wave at 44100
> will not result in a full, finished period of the wave.
> You will have "jumps" at the seams.
>
> play -n synth 10 sin 440 gain -3 dcshift 0.5
>
That was REALLY loud for me - I'm glad my headphones were on the desk!
play WARN alsa: can't encode 0-bit Unknown or not applicable
File Size: 140T
Encoding: n/a
Channels: 1 @ 32-bit
Samplerate: 48000Hz
Replaygain: off
Duration: unknown
In:0.00% 00:00:04.10 [00:00:00.00] Out:193k [!=====|=====!] Hd:0.0
Clip:49.3k
play WARN dcshift: dcshift clipped 49322 samples; decrease volume?
> > The obvious answer is that this pop/crack comes from ALSA,
> > or my DAC or my headphones.
>
> I don't how that's obvious,
> but I cannot replicate the pops and cracks with my SoX.
>
My experience has been that people tend to blame some external entity
rather than the subject of the question - so, I like to try to rule them
out.
> > The only thing that makes me think that it is sox is that the
> > "vol" given to "synth" changes the volume of the pop/crack. If I do, for
> > example:
> > play -r 44100 -n -t alsa synth 0.5 sin 5000 vol -100dB remix 1 1
> > I get nothing but silence.
>
> At -100 dB,there is no audible sound,
> so this is not an example of anything.
>
I had suspected that maybe the act of opening or closing the sound device
might be causing the pop I'm hearing. I believe playing this effectively
silent sound still opens and closes the sound hardware and rules that out?
> I'm taking this as sox being able to open my
> > sound hardware and play the very quiet sound with no pop/crack?
>
> With the line above, you are effectively playing silence.
> There are no pops and cracks in silence.
>
The pop is only at the end - I had suspected that maybe it was the closing
of the sound device/hardware that caused it.
> > I've seen discussion on similar topics where duration of the tone is
> > manipulated to ensure it aligns with write buffers. I suspect that's the
> > problem I am seeing
>
> Mee too.
>
> play -r 48000 -n synth 10 sin 480
>
I had to add "vol -30dB" so as not to deafen myself - this generates the
same pop at the end.
Brian
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