db SPL

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:

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