Detecting whether a 24-bit file has been upconverted from 16-bit? Options

[vincefalks]

I downloaded a FLAC album from online web store and it appears that the files I've downloaded are 24-bit. it's not a hd web store like hdtracks, it's generally a CD 16-bit 44.1kHz store with either FLAC or MP3 to choose from in its offerings.

I'm wondering whether the 24-bit files are real and were supplied as 24-bit from the label and they just didn't label it correctly on the download page, or whether there was an encoding error or just somehow it made its way from 16-bit files to 24-bit FLACs.

Is there a way I can definitively tell or analyze it (looking at spectral maybe) to see if it's been upconverted? Are there certain algorithms and 'good jobs' that can be done to make its 16->24 upconversion undetectable?

happy to upload a sample if it helps.

thanks
vince

[nu774]

Try something like the following to see if wasted bits is equal to or greater than 8 for each FLAC sub-frames.

CODE

flac -ac foo.flac | findstr wasted_bits (for windows)
flac -ac foo.flac | grep wasted_bits (for Unix like OS)

[skamp]

Try something like the following to see if wasted bits is equal to or greater than 8 for each FLAC sub-frames.

Thanks! I used your idea to make a BASH script that prints out the average number of effective bits of FLAC files.

fbits:

CODE

#!/bin/bash

me="${0##*/}"

if [ -w "$TMPDIR" ]; then
tdir="$TMPDIR"
elif [ -w '/tmp' ]; then
tdir='/tmp'
elif [ -w "$HOME" ]; then
tdir="$HOME"
elif [ -w "$PWD" ]; then
tdir="$PWD"
else
echo "$me: error: can't find a writable directory for creating the temporary file" 1>&2 ; exit 1
fi

tf="$( TMPDIR="$tdir" mktemp "${tdir}/${me}.XXXX" 2>/dev/null )"
if [ -z "$tf" ]; then
echo "$me: error: can't create temporary file" 1>&2 ; exit 1
fi

checkbits ()
{
local bps abps tbps=0 n=0
bps="$( metaflac --show-bps "$1" )"
flac -ac "$1" 2>/dev/null | fgrep 'wasted_bits' | cut -d '=' -f 3 | cut -f 1 > "$tf"
while read wb; do
tbps=$(( tbps + ( bps - wb ) ))
((n++))
done < "$tf"
abps=$(( ( ( tbps * 10 / n) + 5 ) / 10 )) # (* 10 + 5) / 10 for proper rounding
printf "%2u/%2u bits\t%s\n" "$abps" "$bps" "$1"
}

for f in "$@"; do
case "$f" in
*.flac) checkbits "$f" ;;
*) continue ;;
esac
done

rm -f "$tf"

Usage:

CODE

fbits *.flac

Output with a lossyFLAC album (Daft Punk - Homework):

CODE

12/16 bits 01. Daftendirekt.lossy.flac
11/16 bits 02. WDPK 83.7 FM.lossy.flac
11/16 bits 03. Revolution 909.lossy.flac
10/16 bits 04. Da Funk.lossy.flac
11/16 bits 05. Phœnix.lossy.flac
10/16 bits 06. Fresh.lossy.flac
11/16 bits 07. Around the World.lossy.flac
10/16 bits 08. Rollin' & Scratchin'.lossy.flac
11/16 bits 09. Teachers.lossy.flac
10/16 bits 10. High Fidelity.lossy.flac
10/16 bits 11. Rock'n Roll.lossy.flac
12/16 bits 12. Oh Yeah.lossy.flac
11/16 bits 13. Burnin'.lossy.flac
10/16 bits 14. Indo Silver Club.lossy.flac
10/16 bits 15. Alive.lossy.flac
11/16 bits 16. Funk Ad.lossy.flac

Output with a "true" 24 bit album (The Beatles - Love):

CODE

23/24 bits 01. Because.flac
22/24 bits 02. Get Back.flac
22/24 bits 03. Glass Onion.flac
23/24 bits 04. Eleanor Rigby ∕ Julia (transition).flac
22/24 bits 05. I Am the Walrus.flac
21/24 bits 06. I Want to Hold Your Hand.flac
22/24 bits 07. Drive My Car ∕ The World ∕ What You're Doing.flac
23/24 bits 08. Gnik Nus.flac
22/24 bits 09. Something ∕ Blue Jay Way (transition).flac
22/24 bits 10. Being for the Benefit of Mr. Kite ∕ I Want You (She's So Heavy) ∕ Helter Skelter.flac
21/24 bits 11. Help.flac
22/24 bits 12. Blackbird ∕ Yesterday.flac
22/24 bits 13. Strawberry Fields Forever.flac
22/24 bits 14. Within You Without You ∕ Tomorrow Never Knows.flac
22/24 bits 15. Lucy in the Sky With Diamonds.flac
22/24 bits 16. Octopus's Garden.flac
22/24 bits 17. Lady Madonna.flac
22/24 bits 18. Here Comes the Sun ∕ The Inner Light (transition).flac
22/24 bits 19. Come Together ∕ Dear Prudence ∕ Cry Baby Cry (transition).flac
22/24 bits 20. Revolution.flac
22/24 bits 21. Back in the U.S.S.R..flac
23/24 bits 22. While My Guitar Gently Weeps.flac
22/24 bits 23. A Day in the Life.flac
22/24 bits 24. Hey Jude.flac
22/24 bits 25. Sgt. Pepper's Lonely Hearts Club Band (reprise).flac
22/24 bits 26. All You Need Is Love.flac

Output with a 16 bit album, upsampled to 24 bits (Daft Punk - Homework):

CODE

16/24 bits 01. Daftendirekt.flac
16/24 bits 02. WDPK 83.7 FM.flac
16/24 bits 03. Revolution 909.flac
16/24 bits 04. Da Funk.flac
16/24 bits 05. Phœnix.flac
16/24 bits 06. Fresh.flac
16/24 bits 07. Around the World.flac
16/24 bits 08. Rollin' & Scratchin'.flac
16/24 bits 09. Teachers.flac
16/24 bits 10. High Fidelity.flac
16/24 bits 11. Rock'n Roll.flac
16/24 bits 12. Oh Yeah.flac
16/24 bits 13. Burnin'.flac
16/24 bits 14. Indo Silver Club.flac
16/24 bits 15. Alive.flac
16/24 bits 16. Funk Ad.flac

[julf]

I used your idea to make a BASH script that prints out the average number of effective bits of FLAC files.

Many thanks! Ran it on my collection of 20,000 tracks, and only found 6 albums showing significant "unused" bits. One, a pure spoken voice one (language training record) had "effective" bits between 13 and 15 depending on the track, 2 CD's (Smoke & Strong Whiskey by Christy Moore and In My Memory by Dj Tiësto) had consistent 15 bits out of 16, and 2 supposedly 24 bit downloads (A Retrospective by The Unthanks and the LSO Haitink Beethoven Symphony no. 9, both from B&W Society of Sound) had consistent 16 effective bits.

The one strange one was Portico Quartet from B&W Society of Sound:

22/24 bits Portico Quartet/Portico Quartet/10 Trace.flac
23/24 bits Portico Quartet/Portico Quartet/01 Window Seat.flac
16/24 bits Portico Quartet/Portico Quartet/02 Ruins.flac
16/24 bits Portico Quartet/Portico Quartet/03 Spinner.flac
23/24 bits Portico Quartet/Portico Quartet/06 Laker Boo.flac
19/24 bits Portico Quartet/Portico Quartet/05 Export to Hot Climes.flac
16/24 bits Portico Quartet/Portico Quartet/09 City of Glass.flac
20/24 bits Portico Quartet/Portico Quartet/08 4096 Colours.flac
22/24 bits Portico Quartet/Portico Quartet/07 Steepless.flac