Flac - Mono Vs. Stereo Options

[Azevedo]

Hey everyone,

I have this audio source in stereo FLAC+CUE and used CUETools (libflake max compression) to split the CUE/FLAC into single tracks
Then, AS THE ORIGINAL CD IS MONO I converted the STEREO FLAC to MONO FLAC using sox:

sox.exe stereo.flac -C 8 mono.flac channels 1

The results:

Stereo:

CODE

Format                                   : FLAC
Format/Info                              : Free Lossless Audio Codec
Duration                                 : 3mn 22s
Bit rate mode                            : Variable
Bit rate                                 : 507 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 44.1 KHz
Bit depth                                : 16 bits
Stream size                              : 12.2 MiB (99%)
Writing library                          : Flake#0.1

Mono:

CODE

Format                                   : FLAC
Format/Info                              : Free Lossless Audio Codec
Duration                                 : 3mn 22s
Bit rate mode                            : Variable
Bit rate                                 : 353 Kbps
Channel(s)                               : 1 channel
Sampling rate                            : 44.1 KHz
Bit depth                                : 16 bits
Stream size                              : 8.51 MiB (100%)
Writing library                          : libFLAC 1.2.1 (UTC 2007-09-17)

Now I have these questions for you folks:

1. After these operations, the mono Flac audio still losslessly 'original'?
2. Why didn't I get 50% space saving when using -C 8 compression level?
3. Is it recommend to scan replay gain and store int on the flac's tag?
4. Is it recommended to encode flac audio in mono out of DUAL MONO?
I mean, dual mono isn't it such a waste?



Thanks

This post has been edited by Azevedo: Oct 20 2012, 14:48

[mjb2006]

Actually it depends on the encoder and settings chosen... libFLAC / flac / flac.exe will not try too hard to figure out the best stereo coding when using the -0, -1, -3, or -4 presets.

I've never seen a CD with mono content that was truly mono (both channels identical). They always ran the mono signal through stereo media or gear on its way into digital, or they dither, so there's always some stereo background noise and slight variations in the channels. This is normally handled very well by mid-side coding. But if the signal is panned the least bit off-center, mid-side coding stops being efficient real quick, so you may find your converted-to-true-mono content compresses better in those situations.

To answer the original question, no, changing a near-mono stereo signal into true single-channel mono is not lossless. It's only lossless if the two channels are identical. However it may actually make the sound more pleasant when you make it true mono. Sometimes the most appealing option is to just take one channel, whichever sounds better to you. Other times you may find it better to combine the channels; this tends to reduce the signal to noise ratio, but may result in some unappealing sound if the non-noise part of the audio is ever out of phase. And sometimes you may prefer not to make things mono at all... I find that when listening with headphones, true mono tends to sound "distant" to me, especially when it's played right after something in stereo. Some stereo noise, however unintentional it may be, actually helps...

This post has been edited by mjb2006: Oct 20 2012, 17:00