Bit Rate

The bit rate is determined by the following settings.

  • Sampling rate
  • Number of channels
  • Codec compression rate
  • Cutoff frequency (for HCA, HCA-MX codec)
  • (For HCA, HCA-MX codec) Bit rate lower limit

The rough calculation method is as follows:

Bit rate [bps] = 16 * Sampling rate [Hz] * Number of channels * Compression rate

The first 16 is the value corresponding to the bit depth. It does not depend on the bit depth of the wav file used, it is always 16.

Note
Even at the same bit rate, the sound quality degrades depends on the codec and configuration parameters.
The numbers listed in this chapter are for reference only. Actual bit rates may differ slightly due to rounding and other factors.

Sampling Rate

The higher the sampling rate, the higher the bit rate. If you want to change the sampling rate without changing the original waveform, specify "Resampling". Please refer to Sampling Rate for details.

Number of Channels

If the number of channels is 2 (stereo), the bit rate will be doubled.

However, if you have specified a low quality setting in the HCA (HCA-MX) codec, the stereo bit rate will be less than half.

This comes from the fact that the compression ratio changes between mono and stereo at low sound quality settings. Specifically, The following applies.

  • The bit rate of stereo at low sound quality (high compression) setting is about 1.67 times that of mono
  • The stereo bit rate at the lowest sound quality (highest compression) setting is 1.5 times that of mono Please refer to Compression Ratio of HCA for details.

Codec compression rate

  • Please refer to Compression Ratio of HCA for the HCA Codec compression rate details.
  • The compression rate of the ADX is about 1/4.
  • For the compression rate of the platform-specific codec provided by each platform, please refer to the document of the corresponding platform.

Cutoff frequency (for HCA, HCA-MX codec)

This setting is valid only for HCA and HCA-MX codecs.

By scraping the sound information higher than the specified frequency, the bit rate decreases. The amount of bit rate change also depends on the sample frequency.

For example, if the sample frequency is 48000 Hz and the cutoff frequency is 15000 Hz, the sound information from 15000 Hz to 24000 Hz is cut, so the bit rate will be 0.625 times as shown below:

15000 / 24000 = 0.625

The following equation can be used when using the cutoff frequency:

Bit rate [bps] = 32 * Cutoff frequency [Hz] * Number of channels * Compression rate

(For HCA, HCA-MX codec) Bit rate lower limit

This setting is valid only for HCA and HCA-MX codecs.

This setting is in the Target config .

The HCA and HCA-MX codecs have a bit rate lower limit set in order to avoid significant deterioration in sound quality.

  • Monaural : 42kbps
  • Stereo : 64kbps

Please refer to the Compression Ratio of HCA for details.

Example of Bit rate

Example 1

When using all 48 kHz stereo sound sources with default settings 

Sampling Rate: 48000[Hz]
Number of channels: 2
Codec: HCA
Sound Quality: Hi Quality
Other: Default

The bit rate in this case is 16 * 48000 * 2 * (1/6) = 256 kbps .

Example 2

If you use a medium quality sound and a cutoff frequency 

Sampling Rate: 48000[Hz]
Number of channels: 2
Codec: HCA
Sound Quality: Medium Quality
Cutoff frequency: 16000[Hz]

The bit rate in this case is 32 * 16000 * 2 * (1/8) = 128 kbps .

Example 3

When high compression is applied to a monaural sound source 

Sampling Rate: 48000[Hz]
Number of channels: 1
Codec: HCA
Sound Quality: Low Quality (Maximum Compression)
Cutoff frequency: 12000[Hz]

The bit rate in this case is 32 * 12000 * 1 * (1/12) = 32 kbps , but it will be 42 kbps since the HCA bit rate lower limit is 42 kbps.
If the lower limit is not to be set, change it in "Bit rate lower limit" of the target configuration.