Electronic music - notes on audio APIs
Contents
Why latency exists (the long version)
Latency and physics
Latency in the real world exists because of distance and the speed of sound.
For some context of how long a millisecond is, and what distance does with sound:
- a mic shoved guitar cab has maybe 1ms to get sound from speaker to mic.
- talking to someone at one or two meters is 3ms to 6ms
- a small-to-moderate music practice space easily has ~15ms of delay from one wall to the other
- opposite ends of a 15m bus would be 40ms
- two frames in 24fps movie are 42ms apart, two frames in 60fps are 17ms apart
- halfway across a sports field is easily 100ms
Which is all physical size divided by the speed of sound. Use wolfram alpha if you're lazy.
So distance alone is
- why bands may well watch their drummers
- why in larger spaces you may want to use headphones instead (but not bluetooth ones)
- one of a few reasons orchestras have conductors
In musical context
Hardware, and the nature of digital audio
Why larger buffers are generally useful
When smaller buffers are required
On drivers and APIs
Windows APIs
Some history
On ASIO wrappers
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
In a practical sense, ASIO usually means "this driver doesn't talk windows sound APIs at all, it talks directly to the sound hardware and to software talking ASIO".
Drivers that speak ASIO often expose only the ASIO API, because much of the point is ignoring all the variation that comes from windows APIs. (yes, also doing windows APIs would be more features, but also be more confusing)
Speaking ASIO to hardware is also called native ASIO, mostly when contrasted with ASIO wrappers.
ASIO wrappers have a different goal.
ASIO wrappers open a regular (non-ASIO) sound card via a regular Windows sound API calls (in practice typically via WDM/KS or Core Audio's WASAPI), force specific settings (e.g. smaller buffers, exclusive mode if possible), then present that via the ASIO API.
Yes, this is counter to ASIO's shortest-path-to-the-hardware principle.
There is still good reason to do it.
ASIO wrappers are usually about pushing underlying hardware to lowest latencies.
- Yes, you will only get latencies that were always possibly to get from that underlying sound API anyway (because that's all you're using).
So why add a layer?
Convenience, mostly.
- it is easier for you to figure out the precise settings (small-buffer, possibly-exclusive) in one place
- in the wrapper's settings, rather than for every DAW-plus-soundcard combination you have
- not only saves work, but the config details vary between DAWs, which can be more fiddly and/or confusing and/or impossible.
- it is easier for programs to talk ASIO than to expose all the very specific API tweaking they gets the something similar
- also not unimportantly, using that wrapper can also be easier to explain to people who care more about music than decades of idiosyncratic programing history.
- There's also some DAWs/software that speak mainly or only ASIO, because their approach is to figure out low latency in something external, and talk to that.
There's a few more useful reasons hiding in the details, like
- you can often force WASAPI cards down to maybe say, 5-10ms without exclusive mode, which means you don't have to dedicate a sound card, to a DAW that only talks ASIO.
- Which is good enough e.g. for when playing some piano on a laptop on the go, so pretty convenient
- some ASIO wrappers can talk to on different sound cards for input and output, at the cost of slightly higher latency (will probably glitch at the lowest latencies), which DAWs talking native ASIO will typically refuse to do (for latency and glitch reasons).
As far as I can tell
- ASIO4ALLv2 is a WDM/KS wrapper.
- needs to force exclusive mode
- can talk to different sound cards for input and output
- FL Studio ASIO (a.k.a. FLASIO) is a WASAPI wrapper.
- Comes with FL studio (including the demo), also usable in other DAWs
- can talk to different sound cards for input and output
- "Generic Low Latency ASIO Driver" is similar to ASIO4ALL but with different options
- Comes with Cubase
- MAGIX ASIO - (verify)
And there appear to also be ASIO multiclient wrappers, basically ASIO in ASIO.
On custom ASIO drivers
In theory, you can write an ASIO driver for any hardware.
It won't do you too much good if the hardware isn't designed for low latency, It won't be one installed automatically, and these days there may be less reason to do so (in that you can get similar latency with Core Audio/WASAPI).
...but e.g. the Kx project, that made a specific series of Sound Blaster cards more capable, also included ASIO support, and would let the cards do on the order of 5ms.
...and I have a handheld recorder that, while fairly cheap, happens to also act as a good low-latency ASIO sound card - when the drivers are installed, anyway.
Some audio interfaces can speak both a regular API and ASIO.
It's more accomodating, but also potentially more confusing, because you cannot talk ASIO while the regular.
And if windows decides it's first in the list of cards, that means you need to poke settings before it does what you think it should.
"So which API is best?"
Linux APIs
Kernel level
Higher level
OSX APIs
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Because OSX was a relatively clean slate at the time, at lower levels there is primarily Core Audio (also present in iOS, slimmed down(verify)), which has been quite capable for a long while.
https://developer.apple.com/audio/
Lowering latency
In general
tl;dr
- zero latency does not exist, a few milliseconds of relative offsets happens all over the place
- amounts of added latency can matter, though
- latency matters when hearing yourself live, or syncing to something live (e.g. looper pedals)
- digital input, output, and/or processing have some latency
- In ways that are (looking at forums) usually partly misunderstood
