Does it ever go over the ceiling?
Not at Output 0 dB or lower and Mix 100 %, with Delta off, Power on and Clip channels on Stereo, the default: no sample leaves SClip above the Ceiling, in every oversampling setting, at any Softness and Foldback, with Link (below where Input stood when you switched it on too) and while Ceiling, Input or Output are automated. No setting turns it off.
Five things lie outside it: the peaks between the samples, which a clipped signal can have (below); what comes after the clipper (next); Power off, your DAW’s bypass and an ended trial, which pass the input unclipped; the Clip channels choices other than Stereo, which clip one part and leave the rest untouched (below); and a DAW’s own oversampling around the plugin, such as REAPER’s per-FX oversampling, whose filter on the way back down can push peaks over again, by up to a few dB. Use SClip’s own oversampling instead: it ends in a stage that holds the filters’ overshoot under the ceiling. From 88.2 kHz up the Oversampling caption names the rate SClip runs at (host 176.4 kHz), so in a 44.1 or 48 kHz project it tells you your DAW oversamples it.
Why do Output, Mix and Delta go past the ceiling?
They come after the clipper, on purpose. Output is a gain on everything, so above 0 dB it raises the clipped peaks with the rest. Mix below 100 % blends in the dry signal, whose peaks were never clipped. Delta is a listening aid: the exact delta is what the clipper removed, which can stand anywhere, and the matched delta follows the output’s height up to 0 dBFS, but for up to 50 ms after you lower the Ceiling it can stand over the new one. Switch Delta off before you render.
Why does my output go over the ceiling in Mid only?
Because Mid only clips the mid alone and lets the side pass untouched. The mid is held at the Ceiling, and then the two go back into the channels: the left is the mid plus the side, the right the mid minus the side. Wherever the side adds to a clipped mid, that channel lands over the Ceiling, and a loud side passes it by itself. Side only, Left only and Right only work the same way: they hold the part they clip, and the rest passes as it came, with no safety clip after it. That is what they are for. The In and Clip meters’ names say which part is clipped (In M and Clip M in Mid only), and the Out meter and the waveform show the overshoot; the waveform draws the ceiling lines faint wherever the signal it shows is not the part held.
For a hard ceiling, choose Both (Stereo) under Clip channels, above Oversampling: once its crossfade has landed, 5 to 25 ms after the change at 48 kHz, no sample passes the Ceiling. To keep what Mid only does and still have a hard ceiling, put a second SClip in Stereo after it (Stereo, mid/side and one-sided clipping).
Why does TP read over 0 dBTP?
SClip’s ceiling holds the samples; with True Peak off, the peaks between them can pass it. Clipping puts peaks between the samples, and those lie higher, so on a track clipped at 0 dBFS the TP number under the loudness, the highest true peak since you last reset it, reads over 0 dBTP. How far depends on Oversampling: Off, typically 0.3 to 1 dB, about 2 to 2.5 dB on a mix clipped 12 dB deep and up to about 4 dB on drums; at 2x and up, typically a few hundredths of a dB, up to about 0.2 dB on a mix clipped 12 dB deep, and at most about half a dB. That is expected: a clipper at 0 dBFS clips there on purpose, so TP keeps its plain color and is there to read, not a warning. TP is the peaks between the samples that a DAC or an MP3/AAC encoder rebuilds, in dBTP (the dBFS scale for them); it only matters for delivery specs. It measures as ITU-R BS.1770 has it, at 4 times the sample rate; from 176.4 kHz up, where the samples already lie that close, it reads the samples themselves. Like any 4x meter it reads hard-clipped material a little under its real peak: in SClip’s tests, 0.3 dB on a hard-clipped 5 kHz sine and 1.2 dB on clipped pink noise. It counts all the time, with SClip’s window closed too, as the other meters do. If a delivery asks for a true-peak limit (−1 dBTP for EBU R 128, −1 or −2 dBTP for Spotify, −2 dBTP for ATSC A/85), switch on True Peak under Oversampling: SClip then holds the true peak under the ceiling too, on music within 0.1 dB on a 16x meter (TP itself, a 4x meter, can still read up to about 0.2 dB over: the ripple of its filter), for 67 samples more latency (112 with Oversampling off at 44.1 and 48 kHz, 97 from 88.2 kHz up). Set the Ceiling to the limit, and meter the master at the end of your chain.
Why does Oversampling Off have one sample of latency?
To round the clip’s corners, Off looks at the next sample before it answers, so its output comes one sample late: 0.02 ms at 48 kHz. A sharp corner makes harmonics above what the sample rate can hold, which fold back down as aliasing, and Off rounds each corner where the signal passes the ceiling by more than 3 dB, in full from 4.5 dB; up to 3 dB it is the plain clip. SClip reports the sample to your DAW, which compensates, and the dry signal of Mix, Delta, Power and your DAW’s bypass is delayed by the same sample, so everything lines up. The oversampled settings take 76 to 83 samples at 48 kHz, 76 to 103 at 44.1 kHz and below, where 4x to 16x use steeper filters, and 61 to 68 from 88.2 kHz up (Oversampling and latency).
What is Foldback?
Wavefolding for what the clipper cuts off: the high band of it, above Frequency, comes back and is folded back under the ceiling, so drums keep their snap. Reflect sets how it meets the ceiling: at 100 % it reflects back under it, quieter and grittier, with harmonics of its own, and darker, with less above Frequency; at 0 % it is held flat on the ceiling, louder and cleaner, with less aliasing, and brighter; values between reflect it partway. Foldback makes harmonics of its own, so give it 2x oversampling or more. At 0 % it does not run.
If it seems to do nothing: it acts only on what SClip clips, so it changes nothing where the signal does not reach the knee; and it lowers the level slightly, up to about 1.6 dB, so compare at the same loudness.
Which methods does SClip use?
Each in plain words first, then the name to look it up by, and what it costs:
- Off’s rounded corners. Where the signal crosses the ceiling between two samples, Off finds the corner on the straight line between them and takes a small correction off both, which rounds the corner: two-point polyBLAMP, from the DAFx 2016 paper “Rounding Corners with BLAMP”. It costs one sample of latency, and on light clipping, up to 3 dB over the ceiling, Off is the plain clip.
- Oversampling. 2x to 16x clip at that multiple of the sample rate between linear-phase half-band FIR filters, which keep the waveform’s shape, so the dry signal of Mix lines up without combing. They cost 61 to 103 samples of latency, by setting and sample rate, and ring faintly just before a sharp hit (pre-ringing).
- The ceiling stage. After the filters, a look-ahead gain turns down the few samples they ring back over the ceiling, smoothly, since a second hard clip there would give back most of the aliasing that 4x and 8x remove. It starts lowering a peak a little before it, within the latency.
- True Peak. A second look-ahead gain, at your project’s rate, reads the signal between the samples at eight times the rate (the midpoint interpolated first, then three points between each pair of those) and holds those peaks under the ceiling too, for 67 samples more latency (112 with Oversampling off at 44.1 and 48 kHz).
- Foldback. What the clipper cuts off goes through a second-order Butterworth high-pass at Frequency, and that band is folded back under the ceiling (wavefolding), or held on it at Reflect 0 %. With Oversampling on it runs at the oversampled rate (at Off, at your project’s rate), and it makes harmonics of its own, so it wants 2x or more.
- The loudness meters. M, S and I follow ITU-R BS.1770-4: its K-weighting (estimated, within 0.05 dB of the exact filters) and the integrated loudness’s two gates; LRA as EBU Tech 3342 has it for EBU R 128; and TP at 4 times the sample rate, as the standard’s Annex 2 does. Like any 4x meter, TP reads hard-clipped material a little under its real peak (above).
- Scope. Each frame ends on the newest rising zero crossing of the signal before the clipper, at the point of the tone’s cycle the last frame held, and the cycle’s length comes from YIN’s difference function, a pitch detector’s.
How much CPU do many instances take?
Little. One instance clipping hard, its window closed, takes 0.04 % of one Apple M4 Pro core at 48 kHz with Oversampling off and 0.12 to 0.32 % at 2x to 16x, the meters and the loudness included, which keep measuring with the window closed. Eighty hard-clipping instances run one after the other as a DAW runs them took 3.5 % of one core at Off and 10 to 27 % at 2x to 16x. Lighter clipping costs less, and so do quieter passages, where TP is not measured since it cannot rise. To see what an instance takes on your computer, open its window: the CPU number in its header is its audio processing while the window is open, the meters included (Performance). An open window costs more than any of that: with music playing it keeps about 31 % of a core busy drawing where the GPU draws, about 24 % where the CPU draws everything, and the drawing and the waveform run only while it is open, so close the windows you are not looking at, or switch them to the compact view.
How do I save power on an older computer?
Switch SClip to the compact view with the button with two small arrows just left of the gear, at the right of the header. The waveform goes away and the transfer graph hides: neither draws anything, and the audio stops feeding the waveform. Every control, the meters and the loudness stay. With music playing on an Apple M4 Pro, the compact view took 14 to 43 % off SClip’s CPU where a Mac’s GPU draws, which draws the meter bars in both views, and about nothing where the CPU draws everything (from a fifth off to an eighth more), in four sets of six rounds. A new SClip opens in the view you chose last on this computer, so you choose it once, and each project keeps the view of each of its SClips (Compact view).
Beyond that, close the SClip windows you are not looking at: the drawing and the waveform then stop entirely, while the meters’ numbers (so the peaks, TP, Clipped %, M max, S max, I and LRA cover the whole song) and Clip to 0’s peak go on being measured, at a small part of their cost. A window covered by others or minimized already draws nothing (on Windows one other window must cover it whole, a menu, a tooltip, a floating panel or a Windows Store app’s window such as Settings or Calculator not counting, and on Linux only a minimized one counts), and on a Mac too slow for every frame SClip updates the displays on every second or third frame by itself.
I hear crackles or dropouts
Raise the audio buffer size in your DAW’s audio settings, for example from 128 to 256 samples. Then set Oversampling lower on the tracks that do not need it (Off suits light clipping) and close the SClip windows you are not looking at.
Clip to 0 is grayed out
Nothing louder than −100 dBFS has played since the peak was last reset, so there is nothing to set Input by, and Peak, in the meters under In, shows −inf. Play the track, with the window open or closed, and the button wakes up. Clicking Peak resets it, and so does a press of Clip to 0, so after a press the button waits until something plays again: the next press goes by what played after the last one. A click does nothing while the button is grayed, but you can already hold it to start Learn, which waits, lit, and learns from the first audio.
The waveform looks wrong or stutters
Under GPU Drawing’s Auto, in Settings, SClip chooses by itself: on a Mac and on Windows the GPU draws the waveform once it has drawn a known picture correctly, and the CPU draws it otherwise, and the GPU draws the meters and the graph; on Linux the CPU draws the whole window. If it still looks wrong, set GPU Drawing to Off: the CPU then draws the meters, the graph and the waveform, at once in every open SClip window, which costs more CPU, and on Windows the system keeps drawing the controls as it always does; Auto chosen again takes effect the next time you open the window. For support only, <VALUE name="gpuRendering" val="gpu"/> in SClip.settings (its place is in the next answer) has the GPU draw without the check: on a Mac and on Windows the waveform, on Linux the meters, the graph and the waveform; never on a graphics setup that draws on the CPU, as in a virtual machine. On a Mac too slow for every frame, SClip updates the displays on every second or third frame; they move at the same speed, in fewer steps.
The window looks wrong, flickers or crashes my DAW when it opens
Some graphics cards and drivers draw SClip’s window wrong. Set GPU Drawing to Off in Settings, and the CPU draws the meters, the graph and the waveform; on Windows the system keeps drawing the controls as it always does. If your DAW crashed as SClip’s window opened on the graphics card, the next window opens as under Off, and a line under GPU Drawing says why; Auto tries the graphics card again once SClip, the graphics driver or the system is updated. If your DAW still crashes every time SClip’s window opens, so Settings is out of reach: quit your DAW, open SClip.settings in a text editor (on a Mac in ~/Library/Application Support/Sonaut Audio/, on Windows in %APPDATA%\Sonaut Audio\, on Linux in ~/.config/Sonaut Audio/) and add <VALUE name="gpuRendering" val="cpu"/> inside <PROPERTIES>, or set that line’s val to cpu where it is there: it is what Off saves. Then email support@sonaut.audio with your graphics card and system version.
What happens when the trial ends?
SClip stays in your projects and passes the signal through unchanged, delayed by its latency, so a track plays on without the clipping and every control stays editable. Power shows as off and the displays dim and hold still, as they do with Power off. The header’s line then opens the Account tab under the gear, where your email address and license key bring the clipping back at once. License has the steps.
The window is too big or too small
Drag the window’s bottom-right corner: SClip keeps its proportions, from half its 100 % size up to what your screen holds. Your project keeps the size, and the next new SClip opens at the size you last gave one. Where the screen has too little room for it, SClip opens as large as fits, keeps its size for a bigger screen and grows back to it once the window is moved where there is room (Settings).
Which formats does it come in?
CLAP and VST3 on macOS, Windows and Linux, and AU on macOS; Install lists the systems. AAX for Pro Tools is in preparation and not available yet. Each takes mono or stereo.
VST is a registered trademark of Steinberg Media Technologies GmbH.
How do I report a bug?
Email support@sonaut.audio with the plugin version, your operating system, your DAW and version, and the steps that trigger the problem. A short screen recording or a crash log helps a lot.