forked from PAWPAW-Mirror/lib_xua
49a116c705
* SDK location can now set in makefile * Mixer requirements added to readme * Uncommented previously broken mixer example from docs as this functionality is now working * Fixed windows build & runtime info in README
252 lines
9.2 KiB
ReStructuredText
Executable File
252 lines
9.2 KiB
ReStructuredText
Executable File
.. _usb_audio_sec_mixer:
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Digital Mixer
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-------------
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The Mixer core(s) take outgoing audio from the Decouple core and incoming audio from the Audio Hub
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core. It then applies the volume to each channel and passes incoming audio on to Decouple and outgoing
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audio to Audio Hub. The volume update is achieved using the built-in 32bit to 64bit signed
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multiply-accumulate function (``macs``). The mixer is implemented in the file ``mixer.xc``.
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The mixer takes (up to) two cores and can perform eight mixes with up to 18 inputs at sample rates
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up to 96kHz and two mixes with up to 18 inputs at higher sample rates. The component automatically
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reverts to generating two mixes when running at the higher rate.
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The mixer can take inputs from either:
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* The USB outputs from the host---these samples come from the Decouple core.
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* The inputs from the audio interfaces on the device---these samples come from the Audio Hub core
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and includes samples from digital input streams.
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Since the sum of these inputs may be more then the 18 possible mix inputs to each mixer, there is a
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mapping from all the possible inputs to the mixer inputs.
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After the mix occurs, the final outputs are created. There are two possible output destinations
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for each mix.
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* The USB inputs to the host---these samples are sent to the Decouple core.
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* The outputs to the audio interface on the device---these samples are sent to the Audio Hub
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core
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For each possible output from the device, a mapping exists to inform the mixer what it's source is.
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The possible sources are the output from the USB host, the inputs from the Audio Hub core or the
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outputs from the mixes.
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Essentially the mixer/router can be configured such that any device input can be used as an input to
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any mix or routed directly to any device output. Additionally, any device output can be derived from
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any mixer output or any device input.
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As mentioned in :ref:`usb_audio_sec_audio-requ-volume`, the mixer can also handle processing or
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volume controls. If the mixer is configured to handle volume but the number of mixes is set to zero
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(such that the core is solely doing volume setting) then the component will use only one core. This
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is sometimes a useful configuration for large channel count devices.
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Control
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~~~~~~~
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The mixers can receive the control commands from the host via USB Control Requests to Endpoint 0.
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The Endpoint 0 core relays these to the Mixer cores(s) via a channel (``c_mix_ctl``). These commands
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are described in :ref:`table_mixer_commands`.
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.. _table_mixer_commands:
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.. list-table:: Mixer Component Commands
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:header-rows: 1
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* - Command
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- Description
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* - ``SET_SAMPLES_TO_HOST_MAP``
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- Sets the source of one of the audio streams going to the host.
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* - ``SET_SAMPLES_TO_DEVICE_MAP``
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- Sets the source of one of the audio streams going to the audio
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driver.
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* - ``SET_MIX_MULT``
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- Sets the multiplier for one of the inputs to a mixer.
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* - ``SET_MIX_MAP``
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- Sets the source of one of the inputs to a mixer.
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* - ``SET_MIX_IN_VOL``
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- If volume adjustment is being done in the mixer, this command
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sets the volume multiplier of one of the USB audio inputs.
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* - ``SET_MIX_OUT_VOL``
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- If volume adjustment is being done in the mixer, this command
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sets the volume multiplier of one of the USB audio outputs.
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Host Control
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~~~~~~~~~~~~
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The mixer can be controlled from a host PC by sending requests to Endpoint 0. XMOS provides a simple
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command line based sample application demonstrating how the mixer can be controlled. This is
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intended as an example of how you might add mixer control to your own control application. It is not
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intended to be exposed to end users.
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For details, consult the README file in the host_usb_mixer_control directory.
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A list of arguments can also be seen with::
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$ ./xmos_mixer --help
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The main requirements of this control utility are to
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* Set the mapping of input channels into the mixer
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* Set the coefficients for each mixer output for each input
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* Set the mapping for physical outputs which can either come
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directly from the inputs or via the mixer.
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.. note::
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The flexibility within this configuration space us such that there is often multiple ways
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of producing the desired result. Product developers may only want to expose a subset of this
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functionality to their end users.
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Whilst using the XMOS Host control example application, consider the example of setting the
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mixer to perform a loop-back from analogue inputs 1 & 2 to analogue outputs 1 & 2.
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.. note::
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The command outputs shown are examples; the actual output will depend on the mixer configuration.
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The following will show the index for each device output along with which channel is currently mapped to it.
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In this example the analogue outputs 1 & 2 are 0 & 1 respectively::
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$ ./xmos_mixer --display-aud-channel-map
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Audio Output Channel Map
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------------------------
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0 (DEVICE OUT - Analogue 1) source is 0 (DAW OUT - Analogue 1)
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1 (DEVICE OUT - Analogue 2) source is 1 (DAW OUT - Analogue 2)
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2 (DEVICE OUT - SPDIF 1) source is 2 (DAW OUT - SPDIF 1)
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3 (DEVICE OUT - SPDIF 2) source is 3 (DAW OUT - SPDIF 2)
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$ _
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The DAW Output Map can be seen with::
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$ ./xmos_mixer --display-daw-channel-map
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DAW Output To Host Channel Map
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------------------------
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0 (DEVICE IN - Analogue 1) source is 4 (DEVICE IN - Analogue 1)
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1 (DEVICE IN - Analogue 2) source is 5 (DEVICE IN - Analogue 2)
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$ _
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.. note::
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In both cases, by default, these bypass the mixer.
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The following command will list the channels which can be mapped to the device outputs from the
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Audio Output Channel Map. Note that, in this example, analogue inputs 1 & 2 are source 4 & 5 and
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Mix 1 & 2 are source 6 & 7::
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$ ./xmos_mixer --display-aud-channel-map-sources
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Audio Output Channel Map Source List
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------------------------------------
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0 (DAW OUT - Analogue 1)
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1 (DAW OUT - Analogue 2)
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2 (DAW OUT - SPDIF 1)
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3 (DAW OUT - SPDIF 2)
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4 (DEVICE IN - Analogue 1)
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5 (DEVICE IN - Analogue 2)
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6 (MIX - Mix 1)
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7 (MIX - Mix 2)
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$ _
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Using the indices from the previous commands, we will now re-map the first two mixer channels (Mix 1 & Mix 2) to device outputs 1 & 2::
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$ ./xmos_mixer --set-aud-channel-map 0 6
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$ ./xmos_mixer --set-aud-channel-map 1 7
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$ _
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You can confirm the effect of this by re-checking the map::
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$ ./xmos_mixer --display-aud-channel-map
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Audio Output Channel Map
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------------------------
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0 (DEVICE OUT - Analogue 1) source is 6 (MIX - Mix 1)
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1 (DEVICE OUT - Analogue 2) source is 7 (MIX - Mix 2)
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2 (DEVICE OUT - SPDIF 1) source is 2 (DAW OUT - SPDIF 1)
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3 (DEVICE OUT - SPDIF 2) source is 3 (DAW OUT - SPDIF 2)
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$ _
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This now derives analogue outputs 1 & 2 from the mixer, rather than directly from USB. However,
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since the mixer is mapped, by default, to just pass the USB channels through to the outputs there will be no
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functional change.
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.. note::
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The USB audio reference design has only one unit so the mixer_id argument should always be 0.
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The mixer nodes need to be individually set. The nodes in mixer_id 0 can be displayed
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with the following command::
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$ ./xmos_mixer --display-mixer-nodes 0
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Mixer Values (0)
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----------------
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Mixer outputs
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1 2
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DAW - Analogue 1 0:[0000.000] 1:[ -inf ]
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DAW - Analogue 2 2:[ -inf ] 3:[0000.000]
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DAW - SPDIF 1 4:[ -inf ] 5:[ -inf ]
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DAW - SPDIF 2 6:[ -inf ] 7:[ -inf ]
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AUD - Analogue 1 8:[ -inf ] 9:[ -inf ]
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AUD - Analogue 2 10:[ -inf ] 11:[ -inf ]
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$ _
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With mixer outputs 1 & 2 mapped to device outputs analogue 1 & 2; to get the audio from the analogue inputs to device
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outputs mixer_id 0 node 8 and node 11 need to be set to 0db::
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$ ./xmos_mixer --set-value 0 8 0
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$ ./xmos_mixer --set-value 0 11 0
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$ _
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At the same time, the original mixer outputs can be muted::
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$ ./xmos_mixer --set-value 0 0 -inf
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$ ./xmos_mixer --set-value 0 3 -inf
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$ _
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Now audio inputs on analogue 1 and 2 should be heard on outputs 1 and 2 respectively.
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As mentioned above, the flexibility of the mixer is such that there will be multiple ways to create
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a particular mix. Another option to create the same routing would be to change the mixer sources
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such that mixer outputs 1 and 2 come from the analogue inputs 1 and 2.
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To demonstrate this, firstly undo the changes above (or simply reset the device)::
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$ ./xmos_mixer --set-value 0 8 -inf
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$ ./xmos_mixer --set-value 0 11 -inf
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$ ./xmos_mixer --set-value 0 0 0
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$ ./xmos_mixer --set-value 0 3 0
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$ _
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The mixer should now have the default values. The sources for mixer 0 output 1 and 2 can now be changed
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using indices from the Audio Output Channel Map Source List::
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$ ./xmos_mixer --set-mixer-source 0 0 4
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Set mixer(0) input 0 to device input 4 (AUD - Analogue 1)
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$ ./xmos_mixer --set-mixer-source 0 1 5
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Set mixer(0) input 1 to device input 5 (AUD - Analogue 2)
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$ _
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If you re-run the following command then the first column now has "AUD - Analogue 1 and 2" rather
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than "DAW (Digital Audio Workstation i.e. the host) - Analogue 1 and 2" confirming the new mapping.
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Again, by playing audio into analogue inputs 1/2 this can be heard looped through to analogue outputs 1/2::
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$ ./xmos_mixer --display-mixer-nodes 0
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