MP3 Format Options
You can adjust MP3 format settings after selecting MP3 format in the Audio Format Options dialog.
(Actually MP3 format is selected in this field by default.)
Basic MP3 settiggs includes the following fields:
Bitrate. Determines the number of bits per second. Bit Rate may be set from 32kb/s to 320kb/s. The default value is set to 128kb/s.
Quality. 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 (less than 160 kbps), high quality for bitrates >160 kbps. The voice quality is more or less optimized to generate the best quality for voice.
Mode. 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.
Forced Stereo: This mode will force MS joint stereo on all frames. It's faster and it uses some special mid and side masking threshold.
J-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.
Mono: This option will forcibly generate a mono file; if the recording audio is in stereo, the input stream will be read as a mono by averaging the left and right channels.
Advensed MP3 settings includes the following fields:
VBR Method. The VBR method setting allows you the change the VBR algorithm which is used for the encoding.
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.
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.
Misc Settings includes the folllowing fields:
MPEG-I/II setting (default value MPEG-I):
The difference between MPEG-I and MPEG-II are the sample frequencies of the input audio stream.
MPEG-I can handle input streams 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.
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.
Frequency (Sampling Rate). Choose the sampling rate for output MP3 files. Auto frequency means that the sampling rate will be choosen automatically.
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