SOLIPSIUMAlpha
SOLIPSIUM Super resolution audio engine
Free loudness checker
Measure integrated loudness, true peak, RMS and noise floor in your browser, then see pass or fail for ACX, Apple Podcasts and Spotify, with what would fix each miss.
Drop an audio file to measure
Measured in your browser. It stays on your device until you ask for a repair.
WAV, MP3, M4A, FLAC and more, up to 30 minutes and 200 MB.
This file is mono. The meter measures the channels present, as BS.1770 does, so it reads about 3 LU lower than the same sound in both channels of a stereo file.
| Check | Yours | Verdict |
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YouTube: commonly measured at about -14 LUFS.
Make audio louder has a free limiter that runs in your browser. It holds the largest sample at -1 dBFS; for ACX's -3 dB, or a true peak below -1 dBTP, set a lower ceiling in your own editor's limiter, then measure the result here again.
Solipsium's free try is built for speech. For music, a free account's editor can run AudioSR on a passage of up to 60 seconds, and what it adds is inferred.
Make a free accountFor a spoken recording, Solipsium can check it in your browser for noise, hum and clipping, then offer to repair its first 20 seconds so you can compare them with the original. The check names noise only when it is loud next to the voice, so it may pass a file that fails ACX's floor.
Solipsium's check in your browser hears recordings of up to five minutes, so this page offers the check and the 20-second try only for those. Make a free account and the editor scans recordings up to 30 minutes.
ACX's peaks are judged on the sample peak, Apple's and Spotify's on the true peak. The noise floor is the RMS of the quietest half second, searched every 10 ms; ACX does not say how it measures either. Each verdict uses the number as shown, to one decimal.
After signing up, drop the same file into the editor to repair all of it.
Then drop the same file into the editor. Scans and short repairs are free.
How it measures
Loudness and true peak follow the published standard, ITU-R BS.1770-5. RMS and the noise floor are the plain measures ACX names.
The sound is weighted the way the standard models hearing, then averaged in 400 ms blocks that start every 100 ms. Blocks under -70 LUFS, and blocks more than 10 LU below the average of the rest, are left out, so pauses do not drag the number down. A mono file is measured as the one channel it has, as the standard does. LUFS and LKFS name the same unit.
The sample peak is the largest sample in the file. The true peak also catches peaks that fall between samples, by looking at the sound four times as finely through the filter in BS.1770-5 Annex 2. Each file is decoded at 48 kHz first, the rate the standard's filter table is written for, so a file saved at another rate is resampled, and its peaks can read slightly differently than in your editor.
RMS is the level of the whole file, unweighted, with every channel counted together: the measure ACX gives its -23 to -18 dB range in. The noise floor is the RMS of the quietest half second, searched every 10 ms. ACX does not say how it measures either, so another checker may read a little differently.
The targets
Quoted from each page as it read on October 15, 2026. The verdicts above use exactly these numbers.
“Each file needs to fall between the specific volume range of -23dB and -18dB RMS for consistent volume.” “Each file must have peak values no higher than -3dB to avoid distortion.” “Each file must have a noise floor no higher than -60dB RMS to avoid background noise distractions.” “Each file must be a 192 kbps or higher CBR, 44.1kHz MP3.”
ACX audio submission requirements“we recommend that the audio signals are preconditioned so the overall loudness remains around -16 dB LKFS, with a +/- 1 dB tolerance, and that the true-peak value doesn't exceed -1 dB FS.”
Apple Podcasts audio requirements“We adjust tracks to -14 dB LUFS, according to the ITU 1770 standard.” “Keep it below -1dB TP (True Peak) max. If your master is louder than -14dB integrated LUFS, keep True Peak below -2dB”
Spotify loudness normalizationYouTube: commonly measured at about -14 LUFS.
Questions
ACX asks for each file to measure between -23 and -18 dB RMS, with peaks no higher than -3 dB and a noise floor no higher than -60 dB RMS, saved as a 192 kbps or higher constant bit rate MP3 at 44.1 kHz and no longer than 120 minutes. This page measures the first three; check the MP3 settings in your export. The full list is on ACX's audio submission requirements.
The quietest half second of the file is louder than -60 dB RMS, usually because of room noise, a fan, hiss or hum under the voice. Turning the file up to reach ACX's RMS range turns that noise up by the same amount, so the noise itself has to come down: record in a quieter room, or clean the recording. When noise is what keeps a spoken recording of up to five minutes from ACX, this page offers to check it for noise, hum and clipping and to repair its first 20 seconds, with no account.
Apple Podcasts recommends about -16 LKFS, plus or minus 1 dB, with the true peak no higher than -1 dB; LKFS and LUFS are the same unit. Spotify adjusts music to -14 LUFS. YouTube is commonly measured at about -14 LUFS.
BS.1770 measures the channels a file has. A mono file is one channel, so it reads about 3 LU lower than the same sound copied to both channels of a stereo file. Some meters count a mono channel twice instead; this one measures the channel that is there.
The checker opens and measures it in your browser and sends none of its audio anywhere. When noise is what keeps a spoken recording of up to five minutes from ACX, the page also offers a check in your browser and then Repair the first 20 seconds; only pressing Repair sends audio to Solipsium, and the note beside the button says exactly what goes.
Drop a spoken recording and Solipsium checks it in your browser, then offers to repair its first 20 seconds for you to compare with the original.
The check and the 20-second try need no account.