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