Audio engineering: minimal audible sound levels

dB Sound Pressure Level (SPL)

Understanding dB by Klark-Teknik Audio System Designer, 2007. Includes voltages and comparisons for dBu and dbV, and frequency SPL tables for human threshold of hearing (with 0dB SPL at 1kHz, for a child or young adult) and SPLs for different typical environments.

Visit also: Wikipedia: Sound pressure

There is a good graph from Monty Montgomery at 24/192 Music Downloads...and why they make no sense:

'Above: Approximate equal loudness curves derived from Fletcher and Munson (1933) plus modern sources for frequencies gt; 16kHz. The absolute threshold of hearing and threshold of pain curves are marked in red. Subsequent researchers refined these readings, culminating in the Phon scale and the ISO 226 standard equal loudness curves. Modern data indicates that the ear is significantly less sensitive to low frequencies than Fletcher and Munson's results.'

You can't compare dbFS even for any alignment convention against dBu or dBV or otherwise vs. dB SPL, but you can test it on various sound systems and listening setups.

Lowest possible audible sounds in dbFS (depends entirely on playback system)

From dBFS vs dB:

'With the K-20 Metering system you set your levels so that -20 dBFS RMS equals 83 dB SPL.'

That would make the minimal audible sound (for a child or young adult) of a 1kHz sine wave around -103 dBFS.

From Dynamic Test Tones (MP3 128kbps, 44.1kHz):

'Each file alternately plays pink noise at a full scale level followed by the same pink noise at a number of decibels below the full scale; the difference is indicated beneath each file. The last file alternates the full scale pink noise with digital silence (mute).

Depending upon your listening environment, as you progress through the series in descending order, you will reach a point at which the alternate tone can be no longer distinguished from digital silence. At that point, the dynamic range available in your environment has been reached.'

However I found these difficult, since the very loud 0dBFS sound followed by a quiet sound made it hard to hear the quiet sound (and the loudest sound was painful at full volume), it would be better to just have the quiet sounds.

So I instead downloaded them and then just played the quiet portion as a selection in Audacity. On my MacBookPro and some quality headphones with Mac volume up highest, I could definitely hear something in the -72dB file, and I could even just barely hear something in a -78dB file that is not listed in the page but can be downloaded by URL.

I decided to go lower, and then first used Audacity to snip out just the quiet portions of the -66dB, -72dB, -78dB files (so I could compare easily in a sequence using Quicktime), and then attenuated the snipped quieter portion of the -78dB file by 6dB to -84dB then -90dB then -96dB:

On my MacBook Pro 17" 2008 laptop, on full, with quality headphones, I could still just hear something, very barely, but definitely, at 84dB. (I could not hear the -90dBFS RMS file at all.)

But nevertheless, on my equipment, there would be no chance at all at getting anywhere near the noise floors in 16-bit, let alone 24-bit, comparing with the following borrowed from ZedBee's super article Digital recording rule of thumb:

Mac OS X: EBU R128 compliant loudness meters and batch processing

FREE EBU R128 meters

These tools are in addition to the FREE EBU R128 ("ebur128") command line loudness filter demonstrated at: A summary of a review of music levels for broadcasting, personal use, recording and mastering, including the new LOUDNESS measures.

FREE from Klangfreund: LUFS Meter:

'EBU R128 compliant loudness measurement

The LUFS Meter plugin enables you to deliver loudness-calibrated content.

Multi-Platform, Multi-Format

Available as VST- and Audio Unit-plugin on Mac. On Windows, the LUFS Meter is available as a VST-Plugin. 32 and 64 bit. Support for Linux and other plugin formats is planned.


Please note that for Audacity you just use 32-bit version, as Audacity does not support 32-bit VST plugins !

I managed to get it to run (preview) a pink noise test file within Audacity:

But it kept crashing Audacity whenever I clicked the Ok button !

Professional paid EBU R128 Meters

Grimm Audio provide a range of professional EBU r128 and ATSC A/85 compatible software and VST, AU, and RTAS plugins.

From LevelView (Price: € 350.00 excl. VAT):

'LevelView is a highly innovative real time loudness meter. Its 'Rainbow meter', based upon the 'Bendy Meter' concept of BBC Research, gives the user continuous insight in recent loudness levels of the program material.

"LevelView is the most innovative real time solution for EBU R128 and ATSC A/85 compliance."


LevelView runs as a plugin in most DAW's on both Mac and PC. There's also a standalone application that directly connects to your sound card.

In trial mode the program has a 14 days evaluation period.'

From LevelOne (Price: € 450.00 excl. VAT ):

'LevelOne offers EBU R128 and ATSC A/85 compatible loudness normalization.


It performs all your level normalization tasks automatically and accurately. You have the choice of normalizing to sample peak, true (over-sampled) peak, PPM peak or ITU/EBU LUFS loudness target levels.


In trial mode the program has a 14 days evaluation period.'

From Waves: WLM Loudness Meter ($400) for Mac or Windows:

'The Waves WLM Loudness Meter plugin provides precision loudness measurement and metering for broadcast, movie trailers, games, packaged media and more. Fully compliant with all current ITU, EBU and ATSC specifications, the WLM offers comprehensive Momentary, Short Term, Long Term, and True Peak readouts ..'

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