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Low latency, multichannel audio with JACK and the emu10k1/emu10k2
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This document is a guide to using the emu10k1 based devices with JACK for low
latency, multichannel recording functionality. All of my recent work to allow
Linux users to use the full capabilities of their hardware has been inspired
by the kX Project. Without their work I never would have discovered the true
power of this hardware.
http://www.kxproject.com
- Lee Revell, 2005.03.30
Until recently, emu10k1 users on Linux did not have access to the same low
latency, multichannel features offered by the "kX ASIO" feature of their
Windows driver. As of ALSA 1.0.9 this is no more!
For those unfamiliar with kX ASIO, this consists of 16 capture and 16 playback
channels. With a post 2.6.9 Linux kernel, latencies down to 64 (1.33 ms) or
even 32 (0.66ms) frames should work well.
The configuration is slightly more involved than on Windows, as you have to
select the correct device for JACK to use. Actually, for qjackctl users it's
fairly self explanatory - select Duplex, then for capture and playback select
the multichannel devices, set the in and out channels to 16, and the sample
rate to 48000Hz. The command line looks like this:
::
/usr/local/bin/jackd -R -dalsa -r48000 -p64 -n2 -D -Chw:0,2 -Phw:0,3 -S
This will give you 16 input ports and 16 output ports.
The 16 output ports map onto the 16 FX buses (or the first 16 of 64, for the
Audigy). The mapping from FX bus to physical output is described in
sb-live-mixer.rst (or audigy-mixer.rst).
The 16 input ports are connected to the 16 physical inputs. Contrary to
popular belief, all emu10k1 cards are multichannel cards. Which of these
input channels have physical inputs connected to them depends on the card
model. Trial and error is highly recommended; the pinout diagrams
for the card have been reverse engineered by some enterprising kX users and are
available on the internet. Meterbridge is helpful here, and the kX forums are
packed with useful information.
Each input port will either correspond to a digital (SPDIF) input, an analog
input, or nothing. The one exception is the SBLive! 5.1. On these devices,
the second and third input ports are wired to the center/LFE output. You will
still see 16 capture channels, but only 14 are available for recording inputs.
This chart, borrowed from kxfxlib/da_asio51.cpp, describes the mapping of JACK
ports to FXBUS2 (multitrack recording input) and EXTOUT (physical output)
channels.
JACK (& ASIO) mappings on 10k1 5.1 SBLive cards:
============== ======== ============
JACK Epilog FXBUS2(nr)
============== ======== ============
capture_1 asio14 FXBUS2(0xe)
capture_2 asio15 FXBUS2(0xf)
capture_3 asio0 FXBUS2(0x0)
~capture_4 Center EXTOUT(0x11) // mapped to by Center
~capture_5 LFE EXTOUT(0x12) // mapped to by LFE
capture_6 asio3 FXBUS2(0x3)
capture_7 asio4 FXBUS2(0x4)
capture_8 asio5 FXBUS2(0x5)
capture_9 asio6 FXBUS2(0x6)
capture_10 asio7 FXBUS2(0x7)
capture_11 asio8 FXBUS2(0x8)
capture_12 asio9 FXBUS2(0x9)
capture_13 asio10 FXBUS2(0xa)
capture_14 asio11 FXBUS2(0xb)
capture_15 asio12 FXBUS2(0xc)
capture_16 asio13 FXBUS2(0xd)
============== ======== ============
TODO: describe use of ld10k1/qlo10k1 in conjunction with JACK
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