Patchbay — audio inputs and outputs

Every audio input and output on the A³ Core’s JACK graph (PipeWire’s, see below): interface, REAPER, beat-analyzer, AES67 and StemDeck. Other pages link here. REAPER’s internal routing is not here. The cables come from ~/.config/rncbc.org/a3-patchbay.xml (QjackCtl, shipped by a3-core; see qjackctl.service), as of 2026-10-08. The maintainer owns the routing and the patchbay; this page only describes them.

The audio interface

The audio server is PipeWire with wireplumber (since 2026-10-14; jackd and a3-jack.service are gone). JACK programs (REAPER, beat-analyzer, StemDeck, QjackCtl) use PipeWire’s libjack, system-wide through /etc/ld.so.conf.d, so a program started by hand finds it too. The USB card (Scarlett, pro-audio profile) drives the graph at 44.1 kHz, quantum 128 (2.9 ms), and appears as the JACK client system:

Direction	Ports	Used for
capture	capture_1 … capture_12	the A³ Mixer’s channels, the phones and the aux return, see REAPER’s inputs 1–12 below
playback	playback_1 … playback_20	Main (playback_1 … 8), Phones (9, 10) and Booth (11 … 18); 19 and 20 are not cabled, see REAPER’s outputs below

REAPER’s inputs and outputs: the channel map

REAPER’s inputs

In	Block	Content
1–8	Analog	decks 1–4, stereo (the A³ Mixer’s channels 1–4)
9–10	Analog	phones
11–12	Analog	aux (the aux return’s analog input, played in ANALOG mode)
13–20	StemDeck	decks 1–4, stereo (StemDeck’s buses 1–4)
21–22	StemDeck	aux
23–30	free

REAPER’s outputs

Out	Block	Content
1–10	Main	1 sub, 2–10 tops; only 1–8 reach the hardware; metered on a copy (out 41–50)
11–20	Booth	11 sub, 12–20 tops; also metered as they are (vu_booth_sub … vu_booth_top9); only 11–18 reach the hardware
21–22	Phones	stereo, to the hardware’s phones outputs; also metered as they are (vu_phones_L, vu_phones_R)
23–24	Rec	stereo, to the audio network (AES67), StemDeck’s rec_L/R and bpm_1; also metered as they are (vu_rec_L, vu_rec_R)
25–26	Aux	the aux return’s analog input (analog 11–12), to the beat-analyzer’s vu_aux_L, vu_aux_R
27–30	free
31–50	VU meters	the analog inputs (31–38) and the Main meters (41–50), to the beat-analyzer, see below
51–66	Channel meters	every channel’s L and R before (51–58) and after (59–66) its fader, to the beat-analyzer

The beat-analyzer’s inputs

Ports	Count	Fed from	Used for
bpm_1	1	REAPER’s rec pair (out23, out24), the first channel of the pair only	tempo detection in clock mode EXT — intern
vu_analog1_L … vu_free70	40	REAPER out 31–50 and 11–26 (see below)	the meters /vu/1–/vu/40
vu_in1_pre_L … vu_in4_post_R	16	REAPER out 51–66	the channel meters /vu/51–/vu/66
vu_stem_a1_L/R … vu_stem_b4_L/R	16	StemDeck’s eight stereo stems (AES67 and/or the local StemDeck); optional, off by default	the stem meters /vu/41–/vu/48

bpm_1 is what the beat-analyzer listens to in EXT (one channel); see Beat Analyzer.

The VU meters: which REAPER out feeds which /vu/n

One JACK input per meter, sent as /vu/n (peak, RMS):

/vu/n	REAPER out
1–20	n + 30 (out 31–50)
21–36	n − 10 (out 11–26)
41–50	none: StemDeck sends them (stem_a1 … stem_b4, stem_aux_L/R)
51–66	n (out 51–66)

/vu/9–/vu/10 and /vu/37–/vu/40 are free placeholders, with no socket. A port name without vu_ is the meter’s name in vu_meters; devices look meters up by it:

REAPER out	beat-analyzer in	beat-analyzer port	OSC	Meter
31–38	1–8	vu_analog1_L … vu_analog4_R	/vu/1–/vu/8	the four channels’ analog inputs, L and R (track “analog”, before any channel processing)
39–40	9–10	vu_free39, vu_free40	/vu/9, /vu/10	free
41	11	vu_main_sub	/vu/11	Main sub
42–50	12–20	vu_main_top1 … vu_main_top9	/vu/12–/vu/20	Main tops 1–9
11	21	vu_booth_sub	/vu/21	Booth sub
12–20	22–30	vu_booth_top1 … vu_booth_top9	/vu/22–/vu/30	Booth tops 1–9
21–22	31–32	vu_phones_L, vu_phones_R	/vu/31, /vu/32	Phones
23–24	33–34	vu_rec_L, vu_rec_R	/vu/33, /vu/34	Rec
25–26	35–36	vu_aux_L, vu_aux_R	/vu/35, /vu/36	the aux return’s analog input, analog 11–12, whatever the return plays
–	37–40	vu_free67 … vu_free70	/vu/37–/vu/40	free, no cable
51–58	–	vu_in1_pre_L … vu_in4_pre_R	/vu/51–/vu/58	the channels’ inputs after TRIM/EQ, L and R
59–66	–	vu_in1_post_L … vu_in4_post_R	/vu/59–/vu/66	the channel buses after the fader, L and R

The beat-analyzer needs NUM_VU_CHANNELS=40 in build/.env (config); it sends five bundles (four of ten, one for stems). Port names: src/audio/vu_ports.cpp. Who shows which meter: The meters.

The stem meters

StemDeck sends its own: /vu/41–/vu/48 (deck A stems 1–4, then deck B), 25 Hz, peak of the louder side and RMS of both, after knob and mute, before fader and buses; plus its AUX bus, stem_aux_L/R (/vu/49, /vu/50).

The beat-analyzer has 16 optional inputs for the same stems (unpatched, off by default), one meter per pair:

beat-analyzer in	beat-analyzer ports	OSC	Meter (vu_meters)
41–48	vu_stem_a1_L/R … vu_stem_a4_L/R	/vu/41–/vu/44	stem_a1 … stem_a4
49–56	vu_stem_b1_L/R … vu_stem_b4_L/R	/vu/45–/vu/48	stem_b1 … stem_b4

NUM_STEM_METERS (default 0; 8 would fight StemDeck’s meters). With them on, NUM_VU_CHANNELS is clamped to 40.

Network audio: AES67

For a StemDeck on another machine, on the audio network (Ports and endpoints, AES67 and PTP). Unit: a3-aes67. Each machine announces its stream by SAP; its JACK ports appear in the graph as a client named after the stream.

Stream	Sent by	Carries	JACK ports
AES67 <hostname> out	Core	12 channels; one stereo pair cabled, the rec pair (REAPER out23, out24) on send_CH1, send_CH2	send_CH1 … send_CH12
AES67 <hostname> stems	StemDeck machine	its buses: 10 stem channels and the cue pair	receive_D1L … receive_AUXR, receive_CUEL, receive_CUER

Only one stereo pair goes onto the Core’s stream: the rec pair, which a remote StemDeck records and OBS streams. Any other pair can go in its place or beside it — booth or main, for example — by cabling it to send_CH3 … send_CH12 in the patchbay; the other machine takes it from its receive_CH… ports.

Nothing connects itself on the StemDeck machine. The StemDeck package ships /usr/share/stemdeck/stemdeck-without-core.xml: load and activate it once in QjackCtl. It cables StemDeck’s buses to its own stream and the Core’s stream to rec_L/R (setup).

On the Core the ten network channels land on REAPER in 13–22:

StemDeck output	Network channel	REAPER in
deck1_L, deck1_R (bus 1)	1–2	13–14
deck2_L, deck2_R (bus 2)	3–4	15–16
deck3_L, deck3_R (bus 3)	5–6	17–18
deck4_L, deck4_R (bus 4)	7–8	19–20
aux_L, aux_R	9–10	21–22

StemDeck’s ports

Ten outputs, its five post-fader buses (deck1 … deck4 are buses, not decks; see StemDeck’s mixer), and two inputs:

Direction	Ports	Arrives on / comes from
out	deck1_L … deck4_R, aux_L/R	REAPER in 13–22
in	rec_L, rec_R	REAPER’s rec pair (out23, out24); feeds REC

StemDeck connects nothing and starts no JACK server; see Audio out.

The patchbay’s sockets as shipped

Ports pair in order; surplus ports stay unconnected. reaper_aux, local_stemdeck and the AES67 sockets exist as both output and input sockets.

Output sockets (what feeds the graph):

Socket	Client	Ports
system_in	system	capture_1 … capture_12
local_stemdeck	StemDeck	deck1_L … deck4_R, aux_L/R
aes67_stems_from_stemdeck	AES67 stream of the StemDeck machine	receive_D1L … receive_AUXR
aes67_cue_from_stemdeck	AES67 stream of the StemDeck machine	receive_CUEL, receive_CUER
reaper_main	REAPER	out1 … out10
reaper_booth	REAPER	out11 … out20
reaper_phones	REAPER	out21, out22
reaper_rec	REAPER	out23, out24
reaper_aux	REAPER	out25, out26
reaper_vu_analog	REAPER	out31 … out38
reaper_vu_main	REAPER	out41 … out50
reaper_vu_channels_pre	REAPER	out51 … out58
reaper_vu_channels_post	REAPER	out59 … out66

Input sockets (what takes audio):

Socket	Client	Ports
reaper_analog	REAPER	in1 … in12
reaper_stems	REAPER	in13 … in22
reaper_aux	REAPER	in9, in10 (no cable)
alsa-scarlett_main	system	playback_1 … playback_8
alsa-scarlett_phones	system	playback_9, playback_10
alsa-scarlett_booth	system	playback_11 … playback_18
local_stemdeck	StemDeck	rec_L, rec_R
reaper_cue	REAPER	in23, in24
aes67_rec	AES67 <hostname> out	send_CH1, send_CH2
beat-analyzer_bpm	beat-analyzer	bpm_1
beat_analyzer_vu_main	beat-analyzer	vu_main_sub, vu_main_top1 … vu_main_top9
beat_analyzer_vu_booth	beat-analyzer	vu_booth_sub, vu_booth_top1 … vu_booth_top9
beat-analyzer_vu_phones	beat-analyzer	vu_phones_L, vu_phones_R
beat-analyzer_vu_rec	beat-analyzer	vu_rec_L, vu_rec_R
beat\-analyzer_aux	beat-analyzer	vu_aux_L, vu_aux_R
beat-analyzer_analog	beat-analyzer	vu_analog1_L … vu_analog4_R
beat-analyzer_channels_pre	beat-analyzer	vu_in1_pre_L … vu_in4_pre_R
beat-analyzer_channels_post	beat-analyzer	vu_in1_post_L … vu_in4_post_R

Cables:

From	→ To	Note
system_in (capture_1 … 12)	reaper_analog (in1 … in12)	the A³ Mixer’s channels, the phones and the aux return
local_stemdeck (10 ports)	reaper_stems (in13 … in22)	local StemDeck
aes67_stems_from_stemdeck	reaper_stems (in13 … in22)	StemDeck on another machine
aes67_cue_from_stemdeck	reaper_cue (in23, in24)	its cue
reaper_main (out1 … out10)	alsa-scarlett_main (playback_1 … 8)	out9, out10 have no hardware output
reaper_booth (out11 … out20)	alsa-scarlett_booth (playback_11 … 18)	out19, out20 have no hardware output
reaper_booth	beat_analyzer_vu_booth	Booth meters
reaper_phones	alsa-scarlett_phones (playback_9, 10)	hardware phones
reaper_phones	beat-analyzer_vu_phones	Phones meters
reaper_rec (out23, out24)	aes67_rec (send_CH1, send_CH2)	the recording mix to the audio network, for a remote StemDeck and OBS
reaper_rec	local_stemdeck (rec_L, rec_R)	local StemDeck
reaper_rec	beat-analyzer_bpm (bpm_1)	the first of the pair
reaper_rec	beat-analyzer_vu_rec	Rec meters
reaper_aux (out25, out26)	beat\-analyzer_aux	aux return meters
reaper_vu_analog (out31 … 38)	beat-analyzer_analog	analog input meters
reaper_vu_main (out41 … 50)	beat_analyzer_vu_main	Main meters
reaper_vu_channels_pre (out51 … 58)	beat-analyzer_channels_pre	channel meters before the fader
reaper_vu_channels_post (out59 … 66)	beat-analyzer_channels_post	channel meters after the fader

Open points

• Main out9, out10 and Booth out19, out20 have no hardware output; the Main and Booth sockets carry ten ports, the interface sockets eight.

• reaper_aux as an input socket (in9, in10) has no cable; the analog phones arrive over reaper_analog, which overlaps it.

• Local StemDeck and the AES67 stems are both cabled to the same REAPER inputs; use one at a time.

• The bpm_1 input takes one channel of the pair only.

• The free meters (/vu/9, /vu/10, /vu/37–/vu/40) have no socket and no cable.