Linux-audio-dev

linux-audio-dev@lists.linuxaudio.org

7513 discussions

by Roger Larsson

http://www.musicdsp.org/ Needs help with their Linux information... Any takers? /RogerL -- Roger Larsson Skellefteå Sweden

22 years, 10 months

Re: [linux-audio-dev] [ann] unmatched - a LADSPA amp tone

by Tom

I'm really late on this one, but I finally looked at the linked waveforms. Here is what I see. Ignoring push-pull crossover distortion, there are basically two kinds of distortion happening. There are two stages to the amplification, a pre-amp and an output amp. The pre-amp provides soft clipping of the input signal, generating harmonics of the input signal. As the input level is increased, the pre-amp output looks more like a square wave but with rounded edges. The pre-amp is outputting at its maximum voltage (saturation). The output amp sees this square wave as a dc step input. The output circuit is under damped, meaning that its step response will include ringing. The frequency of the ringing is related to the design of the output circuitry and has nothing to do with the frequency of the input signal, since the output amp sees its input as dc. The degree of clipping from the pre-amp determines how long the output amp sees its input as a step, and determines how long the output signal contains the ringing. The output amp is not operating at maximum output voltage. This is what allows the overshoot and undershoot spikes in the ringing to pass unclipped. For even more distortion the output amp could be biased to clip the overshoot portion of the ringing. This pseudo-knowledge comes from a distant dream of having studied impulse, step, and ramp responses of analog circuits 20+ years ago. Tom

22 years, 10 months

[linux-audio-dev] USB audio.c driver patch; complete n-channel/24 bit patch

by Monty

Apologies taking time to package this up. The patches included are tested against 2.4.19 or later. This patch fixes a few bugs and implements full n-channel support of greater-than-stereo USB audio devices, such as the emagic emi 2|6. I also opted to make the minor extention to OSS to define 24 and 32 bit AFMT modes, and the patch includes this. It does not break any existing OSS compatability, and unaware apps can continue to be unaware. The modified audio.c will build without the OSS extentions to soundcard.h. As suggested, I didn't bother with OSS mixer extentions. The device I care about most doesn't expose a per-channel mixer feature regardless. Also, I was wrong: 2.5's audio.c is different, but the differences appear to be for the sake of keeping up with other changes to USB support. I did not attempt to apply the included patch to 2.5's audio.c, but I'd give it even odds with sufficient fuzz. Monty

22 years, 10 months

[linux-audio-dev] Re: Music N style sw w/ JACK-support (was: Re: [linux-audio-dev] Re: image problem)

by Patrick Shirkey

Reiner wrote: >> - there's patch for PD that provides JACK-support >> -> >> http://sourceforge.net/mailarchive/message.php?msg_id=1169519 >Actually, this is no longer current. Check the pd list archive for >newer approaches to pd jackification. Personally, I now use Günther >Geiger's patch applied to pd 0.35 and it works quite well. Together >with the plugin~ object for LADSPA plugins the patched pd can be used >as effect rack for ardour. This would make an excellent quicktoot. If you have the time to send me a brain dump I will happily format it. Please consider the benefits that this would provide to pd, ardour and Linux audio users. -- Patrick Shirkey - Boost Hardware Ltd. For the discerning hardware connoisseur Http://www.boosthardware.com Http://www.djcj.org - The Linux Audio Users guide ======================================== "Um...symbol_get and symbol_put... They're kindof like does anyone remember like get_symbol and put_symbol I think we used to have..." - Rusty Russell in his talk on the module subsystem

22 years, 10 months

[linux-audio-dev] Audio Programming

by Lea Anthony

Hi, I am a musician and also a programmer. I have many years experience of coding but not in the audio field. Any tuts around? How do I get into it? Cheers for any info. -Lea.

22 years, 10 months

Re: [linux-audio-dev] [ann] unmatched - a LADSPA amp tone

by nikodimka

>> You can calculate your tranformation for the input signal S(x_i) once >> And the same transformation for S(x_i)+1 again. > >Won't that just give you the gradient at point x_i, ie. d/dt(S)? yes. >We are talking about frequency domain aliasing here, oh yeah i see. sorry. > which is when you >generate partials that would be above the nyquist frequencyi, so they get >reflected down into low frequencies. It is not directly related to the >differential of the signal, though a high differential is often indicative >of an aliasing problem. > >Typically you prevent audio aliasing by generating the waveform in a way >so that it contains no partials above nyquist, or by generating it at a >sufficiently high sample rate that there are none, then decimating down. but you can do the pretty same trick for the frequencies: take two different numbers with no common divisors (or just a pair of prime numbers) as sampling rates and see how the output signal changes. The difference give you some linear combination of aliased frequencies. __________________________________________________ Do you Yahoo!? Y! Web Hosting - Let the expert host your web site http://webhosting.yahoo.com/

22 years, 10 months

Re: [linux-audio-dev] [ann] unmatched - a LADSPA amp tone

by nikodimka

>> my feeling is that oversampling alone will not do, although >> you're probably right in that it will get rid of most of >> the aliasing. > >Its how most people tackle to problem. I think I can get the valve cheap >enough that it will be practical. I'm not really familiar with what are the techniques of anialiasing in use. But I can see the following way. You can calculate your tranformation for the input signal S(x_i) once And the same transformation for S(x_i)+1 again. I mean two similar input signals differing in one bit of value. So when you have two output saignals you can calculate the error due to aliasing: abs( F(S(x_i)) - F(S(x_i)+1) ) And apply some techniques to eliminate this aliasing ranging from qubic splines to plain dithering applied to the output signal. It seems to me that this is much better than oversampling. Especially for nonlinear transformations. (Or is it just a trivial thing and it doesnt work and this is not what you discuss?) nikodimka > >> i'm thinking about how to apply the technique to produce >> square clipping, or better a [0 .. 1] range of clipping, >> but the integration approach is awkward. > >I doubt that the electronics ever produces hard square clips. __________________________________________________ Do you Yahoo!? Y! Web Hosting - Let the expert host your web site http://webhosting.yahoo.com/

22 years, 10 months

Re: [linux-audio-dev] DJCJ Linux Audio Developers Tech Support database.

by Patrick Shirkey

>Well, I just added myself and discovered the first problem - >you can't change anything after you hit that final submit :-\ >I can guarantee that I will be relocating in the next >4 months. No worries. I/we'll have it more configurable by then. >also, I didn't realize that the "Company Name" is necessary >to get the web URL to show up. I haven't taken this scenario into account. I'll look at fixing it. The data is still available I just have to add an if statement. Actually I'm surprised it didn't show up on the preview. >Good idea, I think. Thanks. This is definitely a work in progress. -- Patrick Shirkey - Boost Hardware Ltd. For the discerning hardware connoisseur Http://www.boosthardware.com Http://www.djcj.org - The Linux Audio Users guide ======================================== "Um...symbol_get and symbol_put... They're kindof like does anyone remember like get_symbol and put_symbol I think we used to have..." - Rusty Russell in his talk on the module subsystem

22 years, 10 months

RE: [linux-audio-dev] Re: image problem [was Re: [Alsa-devel] hel p for a levelmeter]

by Patrick Shirkey

> this is what's on the page: >Creative Labs | Soundblaster Live Platinum | EMU10K1 | Install | >(4)[A][B] > bottom of the page: > >(4) Hardware mixing supported > >... > >NOTE: Just because an I/O is listed does NOT mean it is guaranteed to >be supported. Please check the mailing >list archives before making purchase decisions based on requirements >forIEC958 or ADAT I/O. >[A] IEC958 RCA Input >[B] IEC958 RCA Output >which does not have a lot of informational value (I know what it does >not mean but what does it mean?) and it definitely does not imply there >is a problem of getting the docs to support certain functionality. Hmm. It has a certain informational value although I will concede that when I started getting into alsa these comments were cryptic for me then. They assume a certain level of knowledge is known when referring to the notes. I'll try to think of a way to word it for users who may not have the requisite knowledge. Apart from that at the top of the page it's explicitely stated that some companies have not provided the required docs to enable support for a device. I have always noticed those comments however it may just be my angle on things. I have made some changes to the matrix to be more obvious that even if we have the docs we may not have all the necessary parts. Although I would've thought that most people already know that about Linux hardware support. As you know the known bugs section in the driver notes gives explicit information about things that we know do not work. I'll look making a form for adding specifically to this file. I would like to do that and also make it easier for people to post info about supported devices. I have most of the work done but not finished yet. As it is I currently stay up to 6:00 in the morning many nights of the month. I'm lucky though as I only have to work 16 hours a week in my paying job. I could be working many more hours but have made the decision to sacrifice some of my current earnings in order to build Boost Hardware and DJCJ. Along the way I have also picked up the alsa website :) -- Patrick Shirkey - Boost Hardware Ltd. For the discerning hardware connoisseur Http://www.boosthardware.com Http://www.djcj.org - The Linux Audio Users guide ======================================== "Um...symbol_get and symbol_put... They're kindof like does anyone remember like get_symbol and put_symbol I think we used to have..." - Rusty Russell in his talk on the module subsystem

22 years, 10 months

[linux-audio-dev] DJCJ Linux Audio Developers Tech Support database.

by Patrick Shirkey

I'm pleased to anounce that a database for people willing to provide Tech Suppport to their local community has been setup. The service is free of charge and hosted at http://www.djcj.org/ The purpose of this database is to promote the professional arm of the Linux Audio Developers community. It is intended to be of use to potential clients who may be interested in getting a Linux Audio system working but don't have the time or background knowledge to do the installation or system maintainance? The people and businesses presented in the database are not endorsed or guaranteed by DJCJ.org but they are active members of the Linux Audio Community. Payment for services received is encouraged. Rates are decided by the parties involved. This is intended to be a database for professional tech support. Please let people know about it so that we can show the world we are more than just a bunch of amateurs hacking in our spare time. The database currently provides a very simple interface for adding your contact details and there is also a contact form provided for potential clients to easily get hold of you. Special thanks to Steve Harris and Antti Boman for assistance with the internal code. It is guaranteed that the interface will become much more user configurable over time. Any feedback is welcome and appreciated. -- Patrick Shirkey - Boost Hardware Ltd. For the discerning hardware connoisseur Http://www.boosthardware.com Http://www.djcj.org - The Linux Audio Users guide ======================================== "Um...symbol_get and symbol_put... They're kindof like does anyone remember like get_symbol and put_symbol I think we used to have..." - Rusty Russell in his talk on the module subsystem

22 years, 10 months

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Linux-audio-dev