Spectrl
Spectrum, key detection, note frequencies, tonal balance and a system-audio sampler in one window.
Spectrl is a spectrum analyser with the other tools I reach for built in: a note frequency table, key detection, loudness meters, an oscilloscope, tonal balance targets and a system audio sampler, all reading your Mac's audio.
I always have a spectrum analyser open on a second screen, so I thought, why not give it the other things I use all the time, where I can always get at them? I've lost count of how many times I've googled a frequency to note table, and I've downloaded and used a bunch of key detection plugins. Now I don't need them anymore.
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Six tools in one window
The note ruler along the top shows which note a frequency is, and which frequency a note sits at.
Tonal balance draws a corridor over the spectrum showing where mastered tracks in a genre usually sit. It follows your level, so it compares the shape of your mix and ignores how loud it is.
Learn makes a target from any track. Play a reference, press Learn, and its curve becomes the corridor. Save it to use again.
Key detection. Press the button and Spectrl listens for 10 seconds, then guesses the key and scale of your audio and shows how confident it is.
REC records whatever your Mac is playing to a WAV. Point the folder at your Live User Library, or any folder your DAW can see, and the file shows up there. You can also drag it straight out of Spectrl after recording.
Features
- Notes as well as hertz. A note ruler under the spectrum, the nearest note to your cursor in the footer, and exact frequencies on hover.
- Key detection. One press and it listens to ten seconds of audio, then shows the likely key and scale and marks it on the note ruler until you close it. Handy for loops and samples with no key on them.
- Tonal balance targets. Compare what you hear with a target curve, or with your own song using Learn.
- Loudness meters and an oscilloscope, frozen together with the spectrum by one key. Freeze lets you hover for exact values.
- Hold to smooth. Press and hold on the spectrum and the averaging gets 6× longer, so a short peak stays long enough to read. Let go and it's live again.
- Sample anything your Mac plays, in one click. You don't need routing, an aggregate device or a capture app. Press record and Spectrl saves whatever is coming out of your speakers to WAV.
- As light as you need. FFT resolution up to 4K bins and a refresh rate of 30, 15, 8 or 4 fps, for the spectrum and the meters together. Peak detection always uses the full audio stream, so a low rate only costs smoothness. You can leave it open all session next to a heavy set.
- And more. See the manual for the full list.
Why standalone
Spectrl runs as its own app, not a plugin, like a rack analyser that sits beside your gear instead of inside it. It reads your Mac's audio directly, so it works with anything that makes sound, not only your DAW. If your DAW crashes, Spectrl keeps running and keeps what it was recording. If Spectrl has a problem, your session is not affected.
Requirements
macOS 14.4 (Sonoma) or later, on Apple Silicon.
Intel Macs: untested, should work.
The first time it runs, macOS asks for permission to record this computer's audio. Allow it. Without it the screen stays dark and tells you why.
Signed and notarised for macOS.
Version 1.1.0
Privacy
Spectrl only asks macOS for your computer's audio. It doesn't need Screen Recording permission, doesn't use the microphone, and doesn't change what you hear.