EAC --alt-preset standard - Why not Flat 256 bps

vbimport

#1

Hi,

I have a question concerning the compression output when ripping with EAC (Exact Audio Copy) and Compressing with LAME.

Why compress using the --alt-preset standard and not flat 256? The --alt-preset standard compresses the tracks ripped in various bps (Bites) which when checked are not actually correct. When not using the --alt-preset standard and compressing at 256 all the tracks are compressed at an actual 256 when checked.

I checked this by ripping the same Audio CD for both formats which is “AC-DC Volts” all 10 tracks. The disc was clean no scuffs scratches and had never been pulled out of the case till now. The EAC Settings were all the same except for using --alt-preset standard on one rip and flat 256 on the other.

EAC Settings: Used drive : ATAPI CD-RW 32/12/40X Adapter: 1 ID: 1
Read mode : Secure with NO C2, accurate stream, disable cache
Read offset correction : 0
Overread into Lead-In and Lead-Out : No

I used EncSpot MP3 analyzer to verify the actual bit rate of each MP3 track ripped.
http://www.cd-rw.org/software/audio_software/mp3_tools/encspot.cfm

The Results:

RIP: --alt-preset standard

    Bitrates

Actual Claimed


231 500
235 498
239 488
242 593
253 585
133 488
200 509
218 460
226 506
206 468

Total Megs: 89.3mb

RIP: 256

       Bitrates

Actual Claimed


256 256
256 256
256 256
256 256
256 256
256 256
256 256
256 256
256 256
256 256

Total Megs: 105mb

Using the --alt-preset standard takes up 15% less in disc space needed for storage of the track but the quality variant between tracks is allot.

So Why use the --alt-preset standard ?

Anyone have thoughts?

Thanks,

Woody


#2

Well before I answer your question…

Whatever program it is that you pulled those reported bitrates from is reading the VBR bitrates incorrectly.

Now in answer to your question… the reasons to use --alt-preset standard are:

  1. Since it’s VBR, the quality of all the tracks is the same. The bitrate is different because different sounds need different bitrates to be accurately reproduced.
  2. 256kbps is overkill, most of the time. It has been shown experimentally that 192kbps is enough to be transparent for most music, so long as a higher bitrate is used on those occasions that it is really needed.

#3

For a given filesize result, the order of Quality should be:

  1. VBR - uses as much or as little bitrate as required bt the specified quality level.
  2. ABR - Average bitrate, an inbetween step where you want the flexible assignment of VBR, but constrained to a set filesize or average bitrate
  3. CBR - uses the same bitrate for difficult parts as easy ones, with only a limited amount of slip (the bit reservoir) between them.

If you were using something which could display the bitrate allocations in VBR, you’d see it using 320k where it needed to, and less where it didn’t.

The results depend on the material - for a pop record with brickwall limiting and no dynamics, CBR will not be at much of a disadvantage.

Any bitrate quoted for the presets (VBR) is typical/target - the aim of the presets is constant QUALITY, at whatever bitrate the piece demands.

APS aims to be “transparent” (not possible to reliable differentiate from the original) for most material under normal conditions.
Aklt Preset Extreme aims to meet more discerning standards, and typically averages around the 256k bitrate but with better quality.

The next preset up is “Insane” - 320k CBR plus further tunings.