Design the filter.
Then print the page
that goes in the rack.

Why not just a rangefinder?

Because a laser measures distance, and what reaches the audience is time — which includes the amplifier, the processor and the loudspeaker itself, none of which a tape can see.

Two identical clusters, both exactly 30 m from the microphone, on different amplifiers: the tape says they are aligned and they are not. A ported subwoofer is worse. A fourth-order 35 Hz alignment — an ordinary box — carries something like 3.7 ms of its own group delay, which is 1.3 metres the rangefinder cannot reach, and subs are rarely on the same processing as the tops, so nothing cancels.

The real trouble is not that a tape is inaccurate. It is that it cannot reveal its own error — the rig where it is fine and the rig where it is 2.5 ms out look identical until something measures them.

Keep the rangefinder for the cross-check. The metres column should read longer than the tape, never shorter, and the difference is your electronics. Shorter means something is wrong — sound cannot arrive before it left.

It knows which way round the answer goes

You can only ever add delay, so the source that arrives last is the reference and takes none; everything earlier is held back to meet it. Delaying the far source instead of the near one produces numbers that look entirely reasonable and put a tower further out of time than it started.

Every delay is shown in milliseconds and in metres, because a delay is a distance and “the tower is 34 metres behind the main” is something you can check by walking it.

Temperature cannot move it

The delay is a difference between two measured times, and neither was worked out from a distance — both were measured against the loopback. A cold hall and a hot afternoon give an identical answer. Only the metres beside it move.

The seat, drawn

A side view under the impulse: the tops at their height, the sub on the floor, the ref mic standing or seated at its distance. Each line carries its arrival and its distance — 94.10 ms · 30.03 m — and its angle from level near the ref mic. Move the ref mic in the card and the metres and angles follow; the milliseconds are measured and wait for a new sweep.

Sub lands 7.20 ms later. Delay the tops 7.20 ms. That answer needs nothing typed. Give it a laser distance and it adds how much of the gap is where the boxes stand and how much is inside the rack — and refuses a processing time that would have the sound arrive before it could fly there.

The site is shaded by level, red near the boxes to blue far away, with a contour line every 3 dB. Only the ref mic’s spot is measured; the rest is predicted from it, 6 dB per doubling of distance, and says so. Load sample shows all of it without a rig.

The ground, and the level

Ground bounce. Over a narrow low band a reflection off the floor cannot be separated from the direct sound and can pull the arrival late — up to 0.49 ms for tops at 3 m and a standing ref mic 30 m out. The card warns, draws the bounce’s path, and gives the cure: the ref mic on the ground, or a wider band.

What the ground is made of. Measure the ground finds that bounce in the impulse at the moment the geometry predicts and says how much the surface returned — hard, fairly hard or soft — with no table of surfaces needed.

The level at the ref mic. Every sweep reports its level and the room’s in the band read, in dB SPL (Z) once the SPL meter has been calibrated against the organiser’s own meter.

And three things it refuses to do

Each of these produces a delay that looks entirely reasonable and is wrong. So the table groups its rows by microphone position and by band, lowest first, and works out delays only inside a group — the main over low, mid and high, the subs with the main’s low, a tower from its own seat — and never subtracts between them.

• Subtract across two microphone positions Two arrivals from different seats differ by the seat as well as by the source, and no arithmetic separates them afterwards.
• Subtract across two bands A band-limited arrival is the source’s group delay averaged over that band. One subwoofer, one position, read over four bands, gave four arrivals 4.2 ms apart — 1.4 metres of apparent position, from nothing but what was typed in two boxes.
• Align anything measured without a loopback That figure is the driver’s buffers, not a distance, so it cannot be compared with anything — including itself an hour later.

3.15.0 – 3.15.1 — keep the night’s work, and the ref mic’s angle

• Save and open the measurements on their own Every arrival, the layout and the measured ground in a .sonalive file, without the rest of a project — opened again, the listening card and plot come back for review exactly as they were.
• Export CSV One line per arrival for a spreadsheet: band, arrival, distance, delay, levels. One way — the .sonalive file is what reopens.
• Distance and angle on the lines 94.10 ms · 30.03 m on each line, and 2.5° below level near the ref mic. Move the ref mic in the card and the metres and angle move; the milliseconds are measured and wait for a new sweep.
• 3.15.1: the ref mic’s angle 0° is level toward the stage. It changes no timing — only the highs above 5 kHz — and warns when a box arrives far off the mic’s axis over a band that reaches up there.

3.14.0 — what the ground is made of, measured

• No surface table needed How strongly the ground reflects is the surface, and the impulse already holds the reflection. The geometry says when the bounce arrives; Sonasync looks there, and only there.
• How much it returns, octave by octave Measure the ground after sweeping the tops over a wide band: the ground returned 85% of the sound — hard, behaves like concrete, asphalt, tiles or water. Checked through the real measurement chain: a 90% and a 50% bounce read back as 0.900 and 0.500.
• It refuses rather than guesses A band too narrow to separate the bounce, nothing at the predicted moment, or a reflection stronger than any surface returns — each is said, not measured.

3.13.0 — the level across the site, and the ground

• A coverage picture, with contour lines The side view is shaded red near the boxes to blue far away, with a labelled line every 3 dB. Hover anywhere for the level. Only the ref mic’s spot is measured — the rest is predicted from it, 6 dB per doubling of distance, and it says so.
• A warning when the ground bounce can move an arrival No surface data needed: the bounce’s timing comes from the heights and the distance. Tops at 3 m, ref mic at 1.7 m, 30 m out — over 60–150 Hz the arrival can read up to 0.49 ms late on a hard floor. The cure is given: ref mic on the ground, or a wider band.
• dB SPL (Z) Sweep levels say they are unweighted, so they are never read against a limit given in dBA or dBC.
• 3.13.1: Load sample No rig to hand? One button fills the listening plot with a sample tops and sub, marked as sample data everywhere, and one button takes it out again.
• 3.13.2: the band, named The sample sets its own target band, the plot says which band its colours are the level of, and nothing is claimed behind the boxes.
• 3.13.3: where the bounce comes from Behind the boxes is faded rather than blank, and when the ground-bounce warning is on its path is drawn — box, ground, ref mic — with its numbers on hover.

3.12.0 — the sweep’s level, in dB SPL

• How loud it was at the ref mic After a sweep: sweep level 98.4 dB SPL, room 52.1 dB SPL, in the band you read — using the SPL meter’s calibration, and in dBFS, saying so, until it is calibrated. Arrival rows and the listening card carry it too.
• Measured properly for a sweep A sweep only spends part of its time in any band, so an ordinary average reads it several dB low. This one takes the band’s energy over the time the sweep was there — within 0.01 dB of a known sweep.
• Ref mic, by name, and a taller plot The listening card’s fields say Ref mic height and Ref mic distance, and with the plot open the impulse gives it half its height.
• 3.12.1: bands you can see, numbers you can point at The frequency strip shows each box’s band as a bar and the target band before you fire. Hover a bar, a box, the ref mic or anywhere in the view for its real numbers.

3.11.0 — an interface is found when it is plugged in

• Plug it in with the program open The list used to be read at start-up and on Refresh only, so an interface plugged in a minute later was “not detected”. It now appears within a second, and is selected when nothing else is in use.
• A plug elsewhere leaves your measurement alone Headphones or a webcam plugged in mid-sweep no longer stop monitoring. Unplugging the interface in use stops everything on it, and says so.
• Nothing Windows reports is hidden An interface whose input and output were named differently used to be silently missing. Close names now pair when there is only one candidate, and every device left over is listed on the Measure stage with the reason.
• 3.11.1: the listening plot is wide It moved under the impulse in Live IR, full width — frequency up the far left, height up the left in metres, distance across.

Before that

• 3.10.0 — the listening position drawn in Live IR, and the arrivals table grouped by seat and band.
• 3.9.0 — an SPL meter for the wall: subs and tops against their own limits, blinking red over, calibrated against the organiser’s meter.
• 3.7–3.8 — delays the wrong way round are caught; ways that do not reach past their crossover are flagged; a blank plot says why.
• 3.6.0 — Live IR fires one frame at a time; the band is settable from Live IR; it will go below 30 Hz if you ask.
• 3.5.0 — two bands are never subtracted; it listens to the room before it measures; a headroom figure that does not saturate.
• 3.3.0 — the band you type is the band you read; a narrow sweep is scored on the room, not its own width; a refusal names the channel and the cause.
• 3.2.0 — where zero sits on the impulse plot is yours to choose; smoothing on the live transfer function; it says when it is not measuring anything.
• 3.1.x — XTA DP448 joins the processor list; Import can read a filter, and knows which way round it sits.

Each release carries its own notes on the releases page, including the measurements behind the claims above.