Good day.

Default kde volume (tray icon) app, controls the wrong channel of soundcard.
As result, very big volume steps, even one percent step - and sound become very loud.
I cannot choose properly channel for this card, in kde gui mixer control. (Channel for control volume by default)

Before, I try to control via alsamixer, and because understand, that wrong channel, not a software bug, or hardware issue.
Properly channel - PCM or front. But kde mixer force up those channels up to 100% and start to increase "Master" channel. not correct behavior.
Thank you for attention.

Config:
05:00.0 Audio device: Creative Labs EMU20k2 [Sound Blaster X-Fi Titanium Series] (rev 04)
plasmashell --version
plasmashell 5.14.5
darkshvein@lexx9:~$ kf5-config --version
Qt: 5.11.3
KDE Frameworks: 5.54.0
kf5-config: 1.0

sound output: default pulseaudio, Phonon gstreamer.
https://nextcloud.darkshnet.ru/index.php/s/TrcAW9WtrJCBzGr

Your Plasma version is not exactly the newest, maybe try an update first?

Mamarok wrote:Your Plasma version is not exactly the newest, maybe try an update first?

sudo apt install plasma-desktop
Чтение списков пакетов… Готово
Построение дерева зависимостей
Чтение информации о состоянии… Готово
Уже установлен пакет plasma-desktop самой новой версии (4:5.14.5.1-1).
The latest version of plasma-desktop is already installed.

Right, your distribution does not provide a newer version, I understand that, but sadly I can't reproduce your problem here, so unless you test with a newer version, there is little way to know if it is already solved or still a bug. Unfortunately that would mean for you to either use Debian Sid, or change distribution. Currently my HDMI sound output is correct on the newest Plasma release.

Understand that this can vary depending on the hardware and the sound card specifications.