I have bought some music online, delivered in WAV format, presumably highest quality, supposing there was no transcoding happening, but anyway, straight to my question:

My intention is to get at least some minimum understanding of two flac's (man page) options:

  1. -p, --qlp-coeff-precision-search:

    Do exhaustive search of LP coefficient quantization (expensive!). Overrides -q; does nothing if using -l 0.

  2. -e, --exhaustive-model-search:

    Do exhaustive model search (expensive!).

It is absurdly unclear to me, as to just an average music listener, what these settings actually do?

OS + FLAC versions: I am on converting the WAV file to FLAC on Linux Mint 20 (Ubuntu Focal base) with FLAC version 1.3.3.

Several details on original file in WAV format I am testing this on:

file dopamine-remix.wav

RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz

# +

mediainfo dopamine-remix.wav

Complete name                            : dopamine-remix.wav
Format                                   : Wave
File size                                : 86.7 MiB
Duration                                 : 8 min 35 s
Overall bit rate mode                    : Constant
Overall bit rate                         : 1 411 kb/s

Format                                   : PCM
Format settings                          : Little / Signed
Codec ID                                 : 1
Duration                                 : 8 min 35 s
Bit rate mode                            : Constant
Bit rate                                 : 1 411.2 kb/s
Channel(s)                               : 2 channels
Sampling rate                            : 44.1 kHz
Bit depth                                : 16 bits
Stream size                              : 86.7 MiB (100%)

The exact 3 commands I issued for testing purposes were:

# this equals to -8 compression
flac --verify --best --output-name=dopamine-remix--8.flac dopamine-remix.wav

# this equals to -8 -e compression
flac --verify --best --exhaustive-model-search --output-name=dopamine-remix--8e.flac dopamine-remix.wav

# this equals to -8 -e -p compression
flac --verify --best --exhaustive-model-search --qlp-coeff-precision-search --output-name=dopamine-remix--8ep.flac dopamine-remix.wav

Having no idea what different the output is supposed to be(?)

Anyway, I am intentionally not stating how much time these commands took. Please, consider that I do not care about the time spent. For the sake of this question, let's suppose I just want to achieve the best overall compression achievable with FLAC. Thank you.


Okay, it did not come to my mind just to do internet search for flac documentation, by doing this I found the official docu web page.


Exhaustive model search (expensive!). Normally the encoder estimates the best model to use and encodes once based on the estimate. With an exhaustive model search, the encoder will generate subframes for every order and use the smallest. If the max LPC order is high this can significantly increase the encode time but can shave off another 0.5%.


Do exhaustive LP coefficient quantization optimization. This option overrides any -q option. It is expensive and typically will only improve the compression a tiny fraction of a percent. -q has no effect when -l 0 is used.

The second one remains a mystery, though... The provided explanation I find insufficient.

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