Linux-audio-user November 2024

linux-audio-user@lists.linuxaudio.org

7 participants
8 discussions

Tape emulation - is it worth the effort ?

by Fons Adriaensen

Hello all, The purpose of this post is to gather some opinions on the use of 'tape distortion' plugins. The way an analog magnetic tape recorder distorts the signal is quite complicated. The non-linear response is mainly due to the hysteresis of the magnetisation process, and how this interacts with the HF bias added to the recorded signal. Simplifying things a bit, as the tape moves past the recording head and away from it, it goes through several cycles of an hysteresis loop with decreasing amplitude, and it finally converges to some value more or less proportional to the signal. The bias signal itself does not remain on the tape, or at most at a very low level. The same process but with just a very high level HF bias is used to erase the tape. Simulating this accurately is quite complicated, and very CPU intensive. The sample rate must be at least twice the bias frequency (around 100 kHz for 'pro' equipment) and for each sample you need to evaluate the hysteresis loop up to a hundred times (depending on tape speed) to simulate the convergence. Over the past few months I've written the code to do this, with the aim to present a useful 'tape emulation' plugin at the next LAC. It uses a somewhat simplified form of the Preisach algorithm for the hysteresis. <http://kokkinizita.linuxaudio.org/linuxaudio/downloads/preisach-model.pdf> But the first results are somewhat sobering. Have a look at <http://kokkinizita.linuxaudio.org/linuxaudio/downloads/tapesaturation.png> This shows the tranfer function (recorded magnetic signal as a function of the input) for three values of the HF bias. The blue line is what you get without bias. It result in a very smooth saturation for high level signals, but a low amplitude signal will be severly distorted due to the flat region around zero. As bias level is increased, this effect is reduced and the low level gain increases up to some maximum. This is shown by the orange curve. The recommended way to set the correct bias level is to further increase it until the small signal gain is reduced by a few dB (typically 1 or 2 dB, depending on tape type). This is shown by the green curve. The central part of this is very linear (less than 1% THD). But now the smooth saturation is almost transformed into hard clipping. The sharp bend in the curve occurs when the signal amplitude is higher than the bias amplitude. The only effect that remains in a complete simulation is the result of the EQ applied to the signal to be recorded. Higher frequencies have a 'self erasure' effect (which is nicely reproduced by the simulation) and so need to be amplified. The net result is that they will saturate at a lower input level. How much EQ is required depends mainly on tape speed, higher speeds need less. At the most popular 'pro' speed (381 mm/s) this would be something around 10 dB at 10 kHz. At the higher (762 mm/s) speed typically used for 'master tapes' it's just a few dB. So what does effectively remain of the 'smooth saturation and compression' that is claimed to give tape recording its magical 'warm' character ? Is it just a myth ? I also simulated the green curve directly without going through the complicated full simulation, and honestly, to me that sounds just the same. And unless you really use very high levels (much more than would actually be used) the net effect is marginal. Maybe the hard clipping can be useful when applied to individual tracks (e.g. drums or bass), but then there are much simpler ways to do this than 'tape emulation'. Comments invited !!

4 days, 2 hours

Pipewire hard disk usage (presumably)

by Holger Dehnhardt

After the second move this year, I've finally started to set up my home studio properly again. (Ubuntu 24.04.1 LTS, Mixbus, RME ADI-2 Pro for monitoring, Focusrite Scarlett 18i20 2nd generation for integrating analog hardware) Since I've also updated Ubuntu, I've switched my workstation to Pipewire, as I've had quite good experiences with it on my laptop and running several audio interfaces in parallel is quite problematic. My first attempt with a smaller project (17 audio tracks) ran without any problems. My second attempt with a medium-sized project (~30 audio tracks), however, is driving me to despair. I have a DSP load of 50-60%, no buffer underruns but constant stuttering and occasional beeping. The log says the following Nov 12 22:37:13 muse pipewire[2048]: spa.alsa: hw:4c: snd_pcm_mmap_commit error 1022 514 1022: Data transfer interrupted (broken pipe) Nov 12 22:37:24 muse pipewire[2048]: spa.alsa: hw:4c: follower delay:873 target:1536 thr:1024 resample:1, resync (2 suppressed) It is interesting that when I start the safe mode in Mixbus, i.e. all effects are switched off, I have a DSP load of 10 percent and the stuttering and beeping is just as present. I don't have any analog hardware connected at this stage, so I read all tracks directly from disk and send them stereo to the RME interface. I didn't have these problems under jack2, but then the RME was also connected to the Scarlett via TOSLink, so there was only one interface visible to the system. I therefore suspect that it is a problem with the hard disk usage, as I can't think of any other reason. Unfortunately I have not found a way to optimize hard disk access and I don't even know if this is done directly by Pipewire or if one of the usual libraries is used for this. Have you seen this phenomenon before or do you have any ideas what else I can try? Thanks for any suggestions! Holger -- Holger Dehnhardt holger(a)dehnhardt.org https://www.dehnhardt.org

6 days, 4 hours

Pipe organs effect the sound of their halls simply by existing

by David W. Jones

<https://phys.org/news/2024-11-pipe-auto-tune-effect-largest.html> I still don't have a house large enough for a pipe organ. ☹️ --- David W. Jones gnome(a)hawaii.rr.com exploring the landscape of god http://dancingtreefrog.com Sent from my Android device with F/LOSS K-9 Mail.

3 weeks, 2 days

Realtime-Kernel patch merged to mainline kernel after 20 years...

by Tobias Küchel

Cheers to Ingo Molnar! I am not sure how many users are interested in such news, since there might be still a linux-audio-dev community that I am not part of anymore. Nevertheless, it amuses me that basically half my life ago, I struggled and tested and read tons of stuff, invested a lot of time to get some nice audio stuff going on linux and some rather crappy hardware... and now, 20 years later, the foundation to all of it - a real-time kernel - did not disappear but was developed and maintained until the eagle has landed. Again, cheers to Ingo and all that contributed! Yours, Tobias.

1 month

Re: A web-based sound maker

by Mario Lang

"David W. Jones" <gnome(a)hawaii.rr.com> writes: > https://draw.audio/ Also saw that on HN today. In the comments, there was another fun web audio link: https://roland50.studio/ -- CYa, ⡍⠁⠗⠊⠕

1 month

Bach, Mozart or jazz: Scientists provide a quantitative measure of variability in music pieces

by David W. Jones

<https://phys.org/news/2024-11-bach-mozart-jazz-scientists-quantitative.html> --- David W. Jones gnome(a)hawaii.rr.com exploring the landscape of god http://dancingtreefrog.com Sent from my Android device with F/LOSS K-9 Mail.

1 month, 1 week

Behringer FCB1010, or similar

by Worik

Friends I am looking for a MIDI foot pedal board for use with my LV2 simulators (https://github.com/worikgh/120Proof.git) I am considering the Behringer FCB1010 but i am naturally unsure if it is suitable I see on the interweb that it has all sorts of "banks" that can be programmed, but that interests me not What I care about is can I address it from a Linux box, see the MIDI events. Has anybody any experience with this, or recommendations for another product? I am currently using a SINCO pedal from Aliexpress.com that is great, but only has four switches I am keen on more options, and especially the expression peda pedals Worik Sent from Proton Mail Android

1 month, 1 week

[ANN] Qtractor 1.4.0 - A Halloween'24 Release

by Rui Nuno Capela

Hello again, Qtractor 1.4.0 (halloween'24) is out! Change-log: - Improved color contrast on track and clip title labels, when given track foreground and background colors are too similar in lightness. - Clip/Split now also applies to multiple selected clips, on any other track than current, if the split point (play-head) is found within. - Clip Merge/Export... audio clips now taking the internal audio resolution (ie. 64 frames/period), independent to former JACK/Pipewire buffer-size/period. - New Clip Mute state property introduced. - New MIDI clip tool option: Normalize / Compress. - Prepping up next development cycle (Qt >= 6.8) Description: Qtractor [1] is an audio/MIDI multi-track sequencer application written in C++ with the Qt framework [2]. Target platform is Linux, where the Jack Audio Connection Kit (JACK [3]) for audio and the Advanced Linux Sound Architecture (ALSA [4]) for MIDI are the main infrastructures to evolve as a fairly-featured Linux desktop audio workstation GUI, specially dedicated to the personal home-studio. Website: https://qtractor.org https://qtractor.sourceforge.io http://qtractor.sourceforge.net Project page: https://sourceforge.net/projects/qtractor Downloads: https://sourceforge.net/projects/qtractor/files - source tarball: https://download.sf.net/qtractor/qtractor-1.4.0.tar.gz - source package (openSUSE Tubleweed): https://download.sf.net/qtractor/qtractor-1.4.0-6.1.rncbc.suse.src.rpm - binary package (openSUSE Tubleweed): https://download.sf.net/qtractor/qtractor-1.4.0-6.1.rncbc.suse.x86_64.rpm - AppImage [7] package: https://download.sf.net/qtractor/qtractor-1.4.0-6.1.x86_64.AppImage - Flatpak [8] package (thanks Hubert Figuière): https://flathub.org/apps/details/org.rncbc.qtractor Git repos: https://git.code.sf.net/p/qtractor/code https://github.com/rncbc/qtractor.git https://gitlab.com/rncbc/qtractor.git https://codeberg.org/rncbc/qtractor.git Wiki: https://sourceforge.net/p/qtractor/wiki/ - static rendering: https://qtractor.org/doc http://qtractor.sourceforge.net/doc https://qtractor.sourceforge.io/doc - user manual & how-to's: https://download.sf.net/qtractor/qtractor-manual-and-howtos.epub https://download.sf.net/qtractor/qtractor-manual-and-howtos.pdf License: Qtractor [1] is free, open-source Linux Audio [5] software, distributed under the terms of the GNU General Public License (GPL [6]) version 2 or later. References: [1] Qtractor - An audio/MIDI multi-track sequencer https://qtractor.org https://qtractor.sourceforge.io http://qtractor.sourceforge.net [2] Qt framework, C++ class library and tools for cross-platform application and UI development https://qt.io/ [3] JACK Audio Connection Kit https://jackaudio.org [4] ALSA, Advanced Linux Sound Architecture https://www.alsa-project.org/ [5] Linux Audio consortium of libre software for audio-related work https://linuxaudio.org [6] GPL - GNU General Public License https://www.gnu.org/copyleft/gpl.html [7] AppImage, Linux apps that run anywhere https://appimage.org/ [8] Flatpak, next-generation technology for building and distributing desktop applications on Linux https://flatpak.org/ See also: https://www.rncbc.org/drupal/node/2685 Cheers && Keep having (lotsa) fun! - - - rncbc aka Rui Nuno Capela

1 month, 1 week

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Linux-audio-user November 2024