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Subsections

Advanced features

Overriding default settings

 Many of the following features override the encoder's idea of best-quality settings. You should be aware that overriding the encoder default settings is something for experts. You might wreck the encoding quality in a number of ways without first noticing it. Also, the encoder is not guaranteed to run at all parameter combinations. Proceed at your own risk!

-esr 
Output (effective) sample rate.  Usually, the encoder will choose an output  sample rate from 8, 16, 32, or 48 kHz. With some soundcards, it is not possible to play files with sample rates of 48 kHz, others cannot do 32 kHz. With this switch, you can tell the encoder to use another output sample rate.[*]
-dual 
Use dual channel stereo instead of the default mode (see table 2.1). At bitrates of 128 kBit/s and below, this switch will almost certainly decrease the sound quality.
-bw 
Tell the encoder to use another  bandwidth. Increasing the bandwidth from the default setting will work for some signals, but might produces ringing artefacts for others. Use with care! It is not possible to choose bandwidths above half the output sample rate.
-no-is 
Tell the encoder not to use  intensity stereo (see 2.1.3). Some special signals experience susceptible loss of quality if phase information is destroyed; in these cases, you may gain some sound quality using this switch.

Tids & bits

-crc 
For transmission over serial lines with bit errors, parts of the bitstream can be protected by calculating a CRC checksum. If you are just producing for harddisk storage, there is no need to set this switch.
-dm 
To encode at bitrates ranging from 8 to 18 kBit/s, you need a mono input signal. This switch tells the encoder to downmix a stereo input signal into one channel, producing mono output. The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.
-qual 
  This switch controls the tradeoff between fast encoder operation and best sound quality. Table 2.3 gives you an overview which features of the encoder are switched on/off by the -qual  switch. In future versions of the encoder, more features might be controlled by this switch. The only facts you should count on:
  • fastest operation is guaranteed with -qual 0
  • highest encoding quality is reached with -qual 9.[*]


   
Table 2.3: Features controlled by the -qual  switch
Feature Explanation
Soft time-domain filtering Use a high-quality time domain filter instead of fast MDCT
Best match sampling rate Use the best sample rate without regard to filter running time. Adapting to this sample rate might use CPU-intensive filtering.
Full huffman search Find the best huffman code book possible to encode the spectrum of each frame. A few percent bits can be saved in each frame, available for higher quality in following frames.
Many outer loops Shape the quantization noise very carefully.


Footnotes

...rate.
You can also use this switch to match your output sample rate to an integer fraction of the input sample rate to get slightly faster performance

...9.
For some figures on encoding speed see section 2.1.4


layer3@iis.fhg.de, 03/98