[linux-audio-dev] Re: [MusE] More ideas :) [Track freeze] - Alsa Sequencer

[Frank van de Pol]

Hi Jay,

you are right that for good real-time 'play-ability' one wants the latency
as low as possible, but I believe that you didn't get my point that the low
latency should not be achieved at the expense of high jitter. Running a soft
synth with a latency of 10ms would work perfectly OK, though if that same soft
synth had a 10ms jitter it would far for easy be audible. 

Please re-read the original thread. The focus was about providing timestamp
information from sequencer to soft synths to be able to achieve sample
accurate triggering of the events. And also touches some aspects of jitter
vs latency: adding additional (a small bit of) delay might improve the
real-time performance/play-ability of your synth if you can lower the jitter
(at the expense of latency).


On Mon, Jun 16, 2003 at 06:59:40AM +0200, Jay Vaughan wrote:
> 
> >Some of my points of view:
> >
> >- you want the latency (time between user action, eg. tweaking a real-time
> >  control or pressing a key) as low as possible. But don't get trapped in
> >  all the marketing stories people want to play
> >
> 
> I say that this is poor advice.  As a soft-synth developer, one 
> should *ALWAYS* pay attention to latency.  It is one of the key 
> factors (user interface being another) which will sell or kill your 
> app.
> 
> The lower the latency, the better your product will sell - people 
> *DO* notice latency in soft-synths, and regardless of sound quality a 
> high-latency synth plugin will gradually get less and less use.
> 
> Latency is a marketing issue in the synth world because it seriously 
> effects performing/professional musicians' ability to perform. 
> Hobbyist synthesists may not care about latency, and may be fine with 
> pre-rendering everything, but in a performance situation this is not 
> acceptable.

Especially during a live performance the low jitter is important. Musicians
are used to perform with small latency... think about the time it takes
before the sound emitted from a speaker arrives at the ear.

> 
> 
> >  My experience is that even with without low latency it is possible to 
> >  play
> >  an instrument, though is more difficult and takes more practice to get 
> >  the
> >  timing right. A latency of >20 ms makes a piano feel kind of sluggish; a
> >  latency <10ms gives your the feeling of instant sound. The curch organ is
> >  a nice example of an instrument that is difficult to play because of
> >  extremely high latency, but good musicians do manage...
> 
> True, the rule is that good musicians can make music with anything.
> 
> But there's another rule too, and that is that good synth programmers 
> care about and know how to deal with latency in a way which does not 
> interfere with performance ... and can still write amazing 
> synthesizer algorithms without tripping up the latency problem.

But if that programmer receives events from a MIDI port, and has to work
with block/frame based sample audio, things are not that easy anymore. It is
not the latency that wil be your worry but rather the jitter. 

> 
> 
> >  "Recording engineers" who claim that they can't make a decent mix if the
> >  latency is above 10ms might be right with that statement, but I'll be 
> >  glad
> >  to put a bet for a crate of beer on it that they can't do a decent mix
> >  with no latency either ;-)
> 
> I find this to be a highly ungrounded point of view.
> 
> Professional engineers wouldn't use a high-latency synth if it meant 
> it gets in the way of their production.  It's okay for hobbyists who 
> didn't pay a dime for the plugin, but its not okay for professional 
> music production environments where a lot (not just money, but also 
> stress, prestige, and client relationship) is on the line in an 
> average recording session.

If you are talking about extremely high latency like 200ms or more I agree
with you. But if recording engineers are whining that a latency of 10ms is
too high for them to make a mix they better find a new job... 

Remember the velocity of sound waves in air; 10ms is equivalent of your
speakers at 3m distance, not an uncommon thing for a pair of mid-fields.

I feel amost sorry <grin> for those musicians that are playing electric
guitars are are a few meters away from their amps. Not to mention those
realy poor sound engineers doing the live mix for the FOH (front of house)
PA system of an open air concert (distance from mixing desk to FOH for
example 50m; causing a whopping 150ms of latency). Despite all of this,
those magicians do manage to make great sounding music without any concerns
about the latency.

> 
> Linux Audio Developers would do well to keep in mind that latency 
> should never be justified ... there will always be someone else 
> around who doesn't need to justify it.

please remember after me:    J I T T E R

> 
> 
> Us lousy keyboard players may not care about latency, but the kind of 
> pro musician who can really make a difference in the way a market 
> responds to an audio platform does ... and since Linux is a new audio 
> platform, this is pretty important to keep in mind throughout *all* 
> levels of development.
> 
> In my opinion, of course, which isn't worth much ...

I'm just approaching the issue from a different angle, and taking other
aspects in consideration. No need to value any of our opions though. 
I'd be glad to learn from my misunderstandings, that's life for an EE.

> 
> -- 
> 
> ;
> 
> Jay Vaughan
> r&d>>music:technology:synthesizers - www.access-music.de/


I noticed that you are working for Access, and have a vague clue where the
misunderstanding might come from. I presume the Virus DSPs are running the
algoritms blockless, ie. rendering one sample and streaming it to the DACs.
This means that the delay from event reception till sound generation is
constant and virtually without jitter. When compared to the Linux sound
system this would be a luxery situation since the data is always send to the
DACs in small or larger blocks. This block size is reponsible for the
latency, but also might cause jitter if you want to get the signal out the
box as soon as possible.


Frank.


-- 
+---- --- -- -  -   -    - 
| Frank van de Pol                  -o)    A-L-S-A
| FvdPol at home.nl                    /\\  Sounds good!
| http://www.alsa-project.org      _\_v
| Linux - Why use Windows if we have doors available?