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Topic: Newbie questions... (Read 4474 times) previous topic - next topic
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Newbie questions...

Hi! I'm trying out MPC for the first time these few days, and I've got a few questions...

What do the -standard, -xtreme and -insane presets stand for in detail?

Do they include a -scale setting or do I need to add this myself? I saw some of my MPC -xtreme encoded music clipping... :ponder:

Also, I'd like to know what are the kinds of artifacts that MPC might introduce when encoding at low bitrates or when an mpc file is transcoded into mp3.

Thanks

Newbie questions...

Reply #1
Quote
Originally posted by Joe Bloggs
Hi! I'm trying out MPC for the first time these few days, and I've got a few questions...

What do the -standard, -xtreme and -insane presets stand for in detail?


I'm not sure *exactly* which values each switch changes, but the big ones are tmn and nmt.  Unlike with lame though, the mpc presets are very highly tuned and really do not need tweaking unless you wish to go even higher quality than the -insane preset.

There is one small thing you might want though if you use the -standard mode and that is -ltq fil.  This will basically just use a lower ath curve, and the increase in bitrate is negligible.

Quote
Do they include a -scale setting or do I need to add this myself? I saw some of my MPC -xtreme encoded music clipping... :ponder:


There is no default scaling (which is a good thing), however you can choose to scale if you wish, just with the -scale switch.  On most music, encoding normally and just turning on clipping prevention in the decoder will stop almost all clipping, however keep in mind that this will slightly change the sound of the file due to volume differences.  When peforming listening tests to see if the encoding is transparent make SURE you don't have this on.

Quote
Also, I'd like to know what are the kinds of artifacts that MPC might introduce when encoding at low bitrates or when an mpc file is transcoded into mp3.


MPC doesn't really suffer from the type of artifacts you may be thinking of at medium bitrates, and by low bitrates I assume you mean something like lower than 128kbps, which the codec isn't really designed for anyway.  If you want to encode to low bitrates I suggest you use AAC or Vorbis.  At around 128kbps MPC is still pretty good as ff123's test shows (about tied with AAC or maybe very slightly ahead) but below that I'd use something else which was tuned more for those situations.

With the standard mode though, there shouldn't be any blatantly obvious artifacts at all really.

Dibrom

Newbie questions...

Reply #2
Standard profile uses the default values of the encoder, so you don't have to use the standard profile switch if you want to encode using standard profile.
But anyway...

-standard (default values):
-ms 2 -cvd 1 -bw 22050 -ltq ank -ltq_gain 0 -minSMR 0 -tmpMask 1 -tmn 18 -nmt 6

-xtreme:
default except -ltq fil -tmn 20 -nmt 8

-insane
default except -ltq fil -minSMR 3 -tmn 24 -nmt 9

There are also some minor internal switch differencies between profiles which can't be tweaked.
Juha Laaksonheimo

Newbie questions...

Reply #3
Quote
Originally posted by Joe Bloggs

Also, I'd like to know what are the kinds of artifacts that MPC might introduce when encoding at low bitrates or when an mpc file is transcoded into mp3.

Thanks


The kind of artifact MPC introduces is generally extra noise. That usually doesn't cause trouble for mp3 encoders because it's so little.

--
GCP

Newbie questions...

Reply #4
Quote
Originally posted by Joe Bloggs
Also, I'd like to know what are the kinds of artifacts that MPC might introduce when encoding at low bitrates or when an mpc file is transcoded into mp3.

From what I understand of subband coders, the only artifacts you are likely to hear would be quantisation noise and dropouts. These will be caused by over-agressive quantising and masking for lower bitrates.

Newbie questions...

Reply #5
So would it be better to transcode from a 300kbit MPC or a 300kbit AAC?  AAC files at equivalent bitrates seem to have less noise when compared to the original.

-h

Newbie questions...

Reply #6
[deleted]

Newbie questions...

Reply #7
Quote
Originally posted by tangent

From what I understand of subband coders, the only artifacts you are likely to hear would be quantisation noise and dropouts. These will be caused by over-agressive quantising and masking for lower bitrates.


I'm not sure if this is supposed to be the "expected" behavior from subband codecs, but in practice, with MPC this isn't quite the case.

In fact, MPC is the only codec I have seen which doesn't suffer from dropouts.  As far as quantization noise goes, I have heard far more from transform codecs especially on electronic music.  Try encoding something like fatboy, spahm, drone, or even this latest "short" clip with many transform coders and you will hear the effects of this.

At lower bitrates some of this may change, but from what I have heard, at bitrates below 128kbps things just get noisier overall in a more gradual manner, not quite in an abrupt manner.

Newbie questions...

Reply #8
Quote
Originally posted by Dibrom

I'm not sure if this is supposed to be the "expected" behavior from subband codecs, but in practice, with MPC this isn't quite the case.

In fact, MPC is the only codec I have seen which doesn't suffer from dropouts.  As far as quantization noise goes, I have heard far more from transform codecs especially on electronic music.  Try encoding something like fatboy, spahm, drone, or even this latest "short" clip with many transform coders and you will hear the effects of this.

At lower bitrates some of this may change, but from what I have heard, at bitrates below 128kbps things just get noisier overall in a more gradual manner, not quite in an abrupt manner.

Well, I donn't "expect" these artifacts to appear at a high enough bitrate. MPC seems pretty damn well tuned to prevent these artifacts from appearing with a good setting.

I would "expect" these artifacts to start appearing as you drop the bitrate of the MPC encoding I guess.

And if someone told me he heard artifacts in an MPC encoding, I would "expect" it to be quantisation noise, or maybe dropouts.

BTW, do you hear dropouts with those clips using low bitrate MPC?

Newbie questions...

Reply #9
Quote
Originally posted by tangent
And if someone told me he heard artifacts in an MPC encoding, I would "expect" it to be quantisation noise, or maybe dropouts.

BTW, do you hear dropouts with those clips using low bitrate MPC?


I've never heard dropouts from MPC at any bitrate before (that I can remember), not the dropouts that I'm used to hearing in other codecs that is.  The dropouts seem to be more of an artifact related to smearing an encoding error across multiple frames which apparently doesn't happen with MPC due to better time resolution.  This would make sense because MP3 seems to have the most problems with this, while AAC doesn't usually (though it's still not entirely immune).

The quantization noise part is probably more on target, but I believe the nature of it is a little bit different than one might expect.  At increasingly lower bitrates (when starting to go below 128kbps) MPC mostly just starts to take on a "dirtier" sound.. things very gradually become less "clean" and less defined.  This is probably due to the extra noise being introduced.  It's not so much like the quantization noise you might hear in a transform encoder where you get a quick, although harsher, artifact from the noise increasing beyond the ATH for a period of time.

 
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