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patarimai:audio failu kodavimas

xerwer (IP Logged)
May 27, 2004 11:47AM

talpinsiu savo kurinius internete, naudosiu programa cdex lame encoderi 128kbps glaudima. taip pat praverstu ir cd ekstratinimui i harda.

noriu paklaustyti, koki veiksmus pasirinkti, kad kokybes ir garsu praradimai butu iskraipyti maziausiai. kokiems instrumentus kurinyje iskraipo, tai butu lekstesm syntai ar kas?

ka pasirinkit mode join stereo, stereo, forced stereo? ar yra dar kokiu stereo kodavimo rusiu?ju +-?


cdex programa
http://prdownloads.sourceforge.net/cdexos/
http://prdownloads.sourceforge.net/cdexos/cdex_151.zip?use_mirror=umn

siek tiek rasyta, lyg suprantu lyg ne bet yra terminu tokiu, kad niekiap:

his paragraph describes the options for the encoder mentioned above. However, not all options might be available for certain encoders.

Bitrate (default value 128 Kbits/s):

Determines the number of bits per second.

Mode (default value Stereo):

With the LAME encoder, you can specify how the file is encoded. The default stereo option is recommended, but at lower bit-rates, the Joint-stereo or Forced stereo can yield better sound quality.


Stereo: In this mode, the encoder makes no use of potential similarity between the two input channels. It can, however, negotiate the bit demand between both channels, i.e. give one channel more bits if the other contains silence.

Joint stereo: In this mode, the encoder will make use of a correlation between both channels. The signal will be matrixed into a sum ("mid") and difference ("side") signal. For quasi-mono signals, this will give a significant gain in encoding quality. This mode does not destroy phase information like IS stereo that may be used by other encoders. This setting can be used to encode DOLBY ProLogic surround signals.

force joint stereo: This mode will force MS joint stereo on all frames. It's faster and it uses some special mid and side masking threshold.

Mono: This option will forcibly generate a mono file; if the input file is a stereo file, the input stream will be read as a mono by averaging the left and right channels.

Quality (default value Normal):

With the LAME encoder, you can specify the output quality; thus you can trade off encoding time against sound quality. The default (normal) is recommended for the lower bitrates (<160 kbps), high quality for bitrates >160 kbps. The voice quality is more or less optimized to generate the best quality for voice. Details of the R3Mix quality option can be found at http://www.r3mix.net.

MPEG-I/II setting (default value MPEG-I):

The difference between MPEG-I and MPEG-II are the sample frequencies of the input file. MPEG-I can handle input streams (WAV files) with a sample frequency of 48000, 44100 and 32000 Hz. MPEG-II on the other hand will support stream for 24000, 22050 160000 Hz. Basically, use MPEG-II when you want to encode with low bit rates (e.g. for voice files, or if you need small MP3 files with reduced quality). As you can see, the lowest bit-rate for MPEG-II is 8 Kbits/sec while for MPEG-I the lowest bit rate is 32 Kbits/s.

VBR Method Setting

The VBR method setting allows you the change the VBR algorithm which is used for the encoding (detailed information can be found in the LAME user documentation - see http://www.sulaco.org/mp3/doc/html/index.html). The following selections are available

Disabled: Don't use VBR; instead encodie with a Constant Bit Rate (CBR)
VBR-Default: Use the default VBR method (currently set to VBR-MTRH)
VBR-Old: LAME's first functional approach, based on masking, bisection in the bit domain.
VBR-New: LAME's second approach, based on masking and direct noise allocation.
VBR-MTRH: a combination of old and new (VBR) routines
VBR-ABR: The Average Bit Rate (ABR) setting, the encoding principle is similar to what AAC uses as VBR encoding, it is based on perceptual entropy, but more like CBR than VBR. When you select the ABR option in the VBR Settings box, the ABR edit box will be enabled. In this edit box you can specify the target average bit rate. Of course, a larger bit rate will yield generally better-sounding (but larger) MP3 files.

ABR Settings

VBR Quality Setting

This option allows you to set the Variable bit-rate option. Variable bit-rate encoding will enable dynamically determined bit-rates that depend on the music content of the current frame. This improves the overall quality of the encoded file without increasing the file size. This option sets the criteria used to determine when to increase the bit-rate for a frame. The lower the number, the lower the criteria will be. Thus VBR_0 will yield the best quality (but the largest file size) while VBR_9 will have less sound quality but the file size will be the smallest. The recommended variable bit-rate option is VBR_4. If you don't want VBR encoding, set this option to None.

Private

When enabled, it will set the private flag in the MP3 stream.

Original

When enabled, it will set the original flag in the MP3 stream.

Copyright

When enabled, it will set the copyright flag in the MP3 stream.

Checksum

When enabled, it will add a cyclic redundancy check (CRC) code in each frame, allowing [the decoding software] to detect transmission errors that could occur on the MP3 stream. However, it takes 16 bits per frame that would otherwise be used for encoding, and therefore will slightly (probably imperceptibly) reduce the sound quality.
Re: patarimai:audio failu kodavimas
Dalius (IP Logged)
June 02, 2004 12:10PM

xerwer,

Šia tema yra jau tiek daug prirašyta - kad net keista kad dar klausi;-)

Trumpai:
VBR metodas duoda geresnę kokybę nei fixed bit rate, bet jo žymiai mažesnis suderinamumas, todėl jo venk jei nori kad tavo kūrinius be papildomo perkodavimo galėtų klausytis didesnė dauguma (ne tik kompais bet ir nešiojamais MP3 grotuvais ar DVD/CD grotuvais, mokančiais groti ir MP3 failus, iškeptus optiniuose diskuose) bei groti radijo stotys.

Prie 128kbps srauto (Layer 3) siūlyčiau naudoti JointStereo - aukšti dažniai bus natūralesni. Bet tai tik mano nuomonė...

Visa kita - ekspirementuok pats, tik turėk omeny, kad jei tavo garso korta ir akustinė sistema nėra profesionalios - neišgirsi skirtumų tarp daugumos setting'ų (prasti keitikliai kortoje, kaip ir prasti stiprintuvai ir prastos garso kolonėlės irgi užmaskuoja nemažą dalį akustiės informacijos)



Dalius
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