This page contains most essential filter settings and information about current audio playback.
 Output format
This section defines settings for filter output format. AC3Filter will automatically convert any input audio into the configuration specified.
The audio format is characterized by several parameters:
- Speaker layout
- Sample rate
- Sample format
 Speaker layout
At the speaker layout selection you can specify the actual number of speakers and their layout (layout you want to get from AC3Filter). See Speaker layouts for more information about possible outputs.
AC3Filter will convert (mix) any audio into the selected format. When audio format at input differs from the format you choose then filter will add channels or remove some to match the required format. Removed channels will be mixed into the remaining channels (this process is called downmixing). Added channels will be filled with some audio composed from existing channels (this process is called upmixing). See Mixing for more technical details.
It's better to match the channel configuration to the actual number of speakers to make all speakers to work. So, if you have 6 speakers, choose '5.1 (6 channels)'. (You should also set the correct output format at system settings).
If you do not want the filter to change the original number of channels, select 'Do not change'. Note that this feature may not work in some media players and output format will degrade to stereo.
'Dolby Surround/ProLogic' and 'Dolby ProLogic II' modes are required when computer has only stereo output and it is connected to Dolby ProLogic decoder. It is not a multi-channel mode! This is a special type of stereo mode required only if the external Dolby ProLogic decoder is present.
 Sample rate
Sample rate is the number of audio samples sent to the audio card per second. (Read more).
Some audio cards support only the fixed sample rate, so conversion takes place. When you listen AudioCD with 44.1kHz rate using a sound card which supports only 48kHz, Windows does sample rate conversion 44100 -> 48000. But this conversion is not as good as possible. To see the difference between Windows and AC3Filter read Sample rate conversion. To do or not to do?. This article contains actual measures and compares several sample rate conversion algorithms.
Choose the desired sample rate from the list to enable sample rate conversion feature. AC3Filter will convert any audio to the sample rate selected.
 Sample format
Sample format specifies the number of bits per audio sample. More bits, better the quality.
Also, filter proposes 2 floating point formats:
- PCM Float - 32bit floating point format.
- PCM Double - 64bit floating point format.
AC3Filter converts any sample format into the selected one. But you should understand, that when you have 16bit sound at input you cannot make the sound better just by selecting better sample format. Also, if your sound card has 24bit DAC it is no reason to set 32bit to get better quality.
Use SPDIF checkbox switches the digital output mode. This mode is only useful when you have an external decoder/receiver and it is connected using digital (SPDIF) connection. In this case an encoded audio stream will be sent to the receiver without any modifications so receiver decodes and plays it.
Also, filter can encode any input audio into AC3 format and send it to the receiver. It is the only way to playback multi-channel audio using a single SPDIF connection.
This checkbox also shows the current state of SPDIF transmission:
- Filter does not do SPDIF transmission.
- SPDIF passthrough mode
- In this mode, compressed stream is sent over SPDIF without any change. It is impossible to process compressed stream without decompression. Therefore no other filter option can work in this mode (even filter cannot display input/output levels). We cannot even change the sound volume from the computer (only receiver's volume control works).
- SPDIF encode mode
- In this case, input stream is decoded, processed and encoded to AC3 that is sent over SPDIF. Since we have decoded stream in this case, all processing options work. We can change number of channels, volume, etc. before sending the result to the receiver. This allows any stream (even not directly supported by receiver or SPDIF at all) to be sent over SPDIF.
See AC3Filter & SPDIF for more info about this feature.
All filter settings can be recorded as single composition of settings (preset) for fast loading later. There are several standard presets installed together with the filter:
- Standard: No additional processing performed, signal is transferred without any modifications.
- Loud: Maximum loudness.
- Default: this preset is loaded during the filter startup.
You should not use this option instead of player volume or system volume. An overflow and a noticeable decrease of playback quality can take place when high gain level is set.
Master level defines the desirable gain level in dB. If the existing scale is insufficient, you can set the desirable gain level at the field below without any restrictions.
Gain level reflects the current gain level. If there is no overflow then Gain level coincides with the Master level. When an overflow takes place, the automatic gain control system decreases this level. Thus, changing of gain level can indicate too high Master level set.
Refer to Auto gain control and One-pass norm options at Mixer page.
 Dynamic range compression (DRC)
DRC Enabled checkbox switches dynamic range compression feature. The first level defines dynamic range compression level. The second level reflects the current gain level.
 Decoder info
This box displays type and parameters of the current audio stream along with decoder information.
Frames/errors fields reflect the decoder statistics: number of decoded frames / number of error frames.
 Processor usage
This indicator shows the usage of CPU resources by the filter.
Here the current input and output signal levels are displayed. They are shown in a logarithmic (decibels) form. When there is an overflow output level indicators become red. In this case, it is recommended to reduce gain (Master level), since overflow means appearing of distortions.