Linux-audio-dev June 2005

linux-audio-dev@lists.linuxaudio.org

120 participants
101 discussions

by Dave Phillips

Greetings: I ran memtest for a day, the RAM's fine, so I brought in another machine, added my drives, memory, and cards, everything's working all right. Once again I learned a lot, thanks to everyone who replied. But I gotta get me some new iron... Best, dp

19 years, 6 months

[linux-audio-dev] [Slightly OT] How to access "real-time" capabilities

by asbjs＠stud.ntnu.no

This is, I know, slightly off-topic for this group, as it does not deal with audio per se. It does, however, deal with the "real-time"/preemptible Linux kernel, for which I think most of the expertice is gathered here. The OS is Linux, the computer an ordinary PC. The task we are faced with is to run a program, tcpreplay, in such a way that it delivers its network packets as precisely as possible. I.e. the packets should be delivered to the network with the smallest possible timing error. We think that the way to minimize this timing error is to use a kernel with the real-time patches, as this will improve latency and response times. The question is how we can assure that the program really utilizes the real-time capabilities of the kernel. My understanding is that having a real-time capable kernel is only the first step, the second necessary step is to get access to this capabilities? So, how does one accomplish this, given that the program itself does nothing to achieve this? * Will an ordinary program, run as root, take advantage of the real time capabilities of the kernel? * Will an ordinary program, run as a user that is a member of the "audio" group on f.i. Agnula, take advantage of the real-time capabilities? * If given a real-time kernel, what else is necessary to take advantage of its capabilities? * How does normal priorities (nice, renice) play together with the real-time kernel? With kind regards Asbjørn Sæbø

19 years, 6 months

[linux-audio-dev] sample browsing app

by mimo

After my initial problems with jack I must say I have come to like jack. Especially together with muse. Now I wonder, is there something like a sample browser (possibly with jack output) that allows traversing through directories and click-n-play audio files in them? Something like good old fastwav on windows... I have searched and searched but everything I could find needs at least two clicks to play.. also kde/qt drag and drop would be nice.. thanks, mm

19 years, 6 months

Re: [linux-audio-dev] [ot] [rant] gcc, you let me down one time toomany

by eviltwin69＠cableone.net

On Thu, 9 Jun 2005 10:05 , 'Chris Cannam' <chris.cannam(a)ferventsoftware.com> sent: >N Smethurst: >> Since a vector is a wrapped C array (i.e. contigous), the [] operator >> compiles to the C equivalent when optimisation is turned on. > >I was thinking of iterator operations, having vaguely recalled that the vector iterator in the gcc library had at some point changed from an actual pointer to a wrapper class. Looking at the code, though, the wrapper is so thin that it probably isn't an issue with optimization on. > > I was under the impression that there was bounds checking going on with vectors. Is this not the case? Jan

19 years, 6 months

[linux-audio-dev] [ot] [rant] gcc, you let me down one time too many

by Tim Goetze

Frailty, thy name is GCC A Modern Drama in Three Scenes. Dramatis Personae: An ardent programmer and a popular C++ compiler -*- Prologue: Appalled by the rat race commonly known as the proprietary software business, our young and gifted hero joins the light side, deeply inspired by the manifold yet subtle qualities of free software. Scene I: Our hero in day-and-night-long sessions optimizes the hell out of a SSE2-based n*4-band IIR equalizer. Of course in assembly, and mixed with C++ templating. The final code is about 10% faster than floats on AMD, probably a fair bit quicker yet on P4 systems. Enter gcc version 3, which drops multi-line inline assembly support. Said assembly code becomes effectively unusable and dies a quick and unsung death. Scene II: Our hero puts years of work into an all-round realtime audio and MIDI library that expands the Python programming language. While having its flaws, it's a versatile, surprisingly stable and immensely capable system, partly thanks to a very clever (according to our hero) design that subclasses Python's C types in C++. Enter gcc version 3, moving the vtable member to memory offset 0 of a derived type even if the base type is in C which doesn't know about vtables. As a result, the very foundation of said library's type system is rendered nonfunctional since Python expects its type header to reside in the very same memory location. With no precautions for such an abrupt change taken and the implications requiring a manual review and substantial rewrite of a good 50.000 lines of source code, said library dies a slow and painful but equally unsung death. Scene III: Our hero bundles his DSP efforts into a free plugin library, once again saving himself much work and improving code readability by using C++ templates, resulting in quite an elegant object system and source code, hethinks. Enter gcc version 4, which requires the templated types' constructor code be rewritten in the most nonsensical, misleading and ugly fashion possibly imaginable this side of Hungary and Redmond, WA, according to our (now not so very young anymore) hero. Epilogue: Our hero has completely and permanently lost his faith in the popular compiler. Disillusioned and indecisive, he resigns himself to henceforth reluctantly write C++ only to support his miserable life. His plight is so bad he downright refuses to support the latest follies of the popular compiler in his free software efforts. -*- Will this be the end? To be continued, hopefully. Cheers, Tim

19 years, 6 months

Re: [linux-audio-dev] [ot] [rant] gcc, you let me down one time toomany

by eviltwin69＠cableone.net

On Thu, 9 Jun 2005 23:41 , David Cournapeau <cournape(a)gmail.com> sent: >On 6/9/05, stefan kersten steve(a)k-hornz.de> wrote: >> On Thu, Jun 09, 2005 at 10:31:35PM +0900, David Cournapeau wrote: >> > _Z6vectorSt6vectorIiSaIiEE: >> > .LFB539: >> > .L2: >> > .L7: >> > pushl %ebp >> > .LCFI0: >> > movl %esp, %ebp >> > .LCFI1: >> > popl %ebp >> > ret >> > >Well, that's what happens when one post some code after some heavy >coding all day long, and when one tries to answer two questions at the >same time....That's why I would have prefered to find the relevant >part instead in the C++FAQ :) > > Anyway, for the question "is there bound checking with operator[]", >the answer of Bjarne Stroustrup is no :). > The other problem "is [] as efficient for vector and plain c array >?", well, people who know better than me asm/gcc can test and answer. > Yeah, it really needs to be tested to tell. I remember taking a course in VAX Macro asm back in the days of dinosaur eggs and phonograph needles. The book, DEC, and the teacher all said you could turn off the VAX debugging mode when you compiled. I wrote some self-modifying code for one of the exercises (I wouldn't do that in real life ;-) The compiler still slapped in some debugging stuff and it wouldn't work. It was a real simple program though so the instructor checked it and passed it anyway ;-) Jan

19 years, 6 months

Re: [linux-audio-dev] [ot] [rant] gcc, you let me down one time toomany

by Chris Cannam

Jan Depner: > I was under the impression that there was bounds checking going on with > vectors. Is this not the case? Nope. Chris

19 years, 6 months

Re: [linux-audio-dev] [ot] [rant] gcc, you let me down one time toomany

by Chris Cannam

N Smethurst: > Since a vector is a wrapped C array (i.e. contigous), the [] operator > compiles to the C equivalent when optimisation is turned on. I was thinking of iterator operations, having vaguely recalled that the vector iterator in the gcc library had at some point changed from an actual pointer to a wrapper class. Looking at the code, though, the wrapper is so thin that it probably isn't an issue with optimization on. Chris

19 years, 6 months

[linux-audio-dev] Re: Software controller for homemade edrums

by Kevin Sookocheff

>Could anyone point me toward a document explaining the >technical/mathematical details of convolution, especially about audio? I've used convolution/correlation/fourier analysis for school projects. The standard text for Fourier analysis is Bracewell, "The Fourier Transform and its Applications". Also check out "Numerical Recipes in C" (available on-line) by Press, Teukolsky, Vetterling and Flannery, Cambridge Press, for code on performing convolution and correlation with the fast fourier transform. As for audio, I've dealt mostly with images but the same principals apply. Audio is a 1D signal and most texts spend a considerable time covering these . Look for any book on digital signal processing and it will most certainly contain what you need. Kevin

19 years, 6 months

Re: [linux-audio-dev] Re: Software controller for homemade edrums

by Ben Loftis

> And, as I said above, it did work better with some samples than with > others, but: it works :-) > > Here are three example of what it sounds like, using a modified guitar > chord sample as response file : > > 1 - For this one I softly hit the edge of the pad continuously, and the > middle of the edge harder once at the beginning of the measure : > http://samalyse.com/labs/edrum/audio/beat.ogg > > 2 - Playing faster ("rolling") with this one : > http://samalyse.com/labs/edrum/audio/roll.ogg > > 3 - Using a pen to hit and scratch the surface. The rubber surface, made of > several layers of bike tube makes it possible to obtain an interesting > sound (the input level was not high enough for this one, so I normalized it > afterward, it could sounds much better I think) : > http://samalyse.com/labs/edrum/audio/scratch.ogg > > As you may see, scratching seems to work fine in here :-) > This is so incredibly cool! Is this technique already in wide use somewhere that I missed? Because if not, it should be. This means that all you need for an electronic drum set is a multichannel sound card and some homemade piezo-triggered pads! And I think with some further experimentation with pad materials and response files, you can probably come up with all kinds of permutations on the sound. I'd like to hear what this sounds like using some traditional drum samples ( like a snare or an 808-style kick ). I'm assuming that the current samples lack "punch" only because they are from a piano chord response file. > By the way, Ben, what do you think of my idea of coupling triggering with > convolution, as stated in my previous mail (above, third paragraph) ? > Here's a diagram to further describe this idea : > > pad signal ----> trigger detection ----> sample playback ----- > | | > | | > -------------------------------------> convolution <---- > | > | > +--> output > > Would this be possible ? You essentially _have_ the drawing, above. You just can't change the sample on every hit. I don't know what you expect to achieve. Trust me, what you've got now is much cooler than a triggered playback (although it does not sound the same) It is possible that using a triggered sample or some sort of envelope follower will be required to get the attack of a traditional drum sound. I'm sure there are lots of ways to improve this simple system beyond jack_convolve. I think you've stumbled across a really cool synthesis technique! -Ben

19 years, 6 months

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Linux-audio-dev June 2005