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= Audio Filters =
The release of AllStarLink 1.01 software package contains a feature pioneered by Jeff DePolo, WN3A. It is a set of audio filters for amateur radio applications. The default transmit and receive filters were designed around commercial standards. However, because amateur radio operators have the resources to use wider bandwidths, especially on UHF, they may prefer other filter types in order to provide higher audio quality. Over the years there have been other fixes for the usbradio channel driver minimizing the distortions. The results below proves the distortions are considerably lower than what a typical radio/repeater will add into the audio chain (.8% for the application vs. 3 to 5% or more for the radio). Contrary to what you may have read elsewhere, the dynamic range of this application, when properly deployed, is far beyond the capabilities of wide-band FM radio.
The release of AllStarLink 1.01 software package contains a feature pioneered by Jeff DePolo, WN3A. It is a set of audio filters for amateur radio applications.
The following settings can be optionally used in a USB radio interface context in "/etc/asterisk/usbradio.conf". If these keyword and value pairs are not present, their values default to zero (0). These alternate filters should be used with care. Note that additional computing power and radio adjustments may be necessary depending on your application. They have been extensively tested and work fine even with the Raspberry Pi3. Unlike other distributions, we encourage the use of the usbradio channel driver (chan_usbradio), or what we commonly call "Full DSP" in AllStarLink 1.01. This feature will also work in simpleusb, if that's what you prefer.
The default transmit and receive filters were designed around commercial standards. However, because amateur radio operators have the resources to use wider bandwidths, especially on UHF, they may prefer other filter types in order to provide higher audio quality. Over the years there have been other fixes for the [[Usbradio.conf|usbradio]] channel driver minimizing the distortions. The results below proves the distortions are considerably lower than what a typical radio/repeater will add into the audio chain (.8% for the application vs. 3 to 5% or more for the radio). Contrary to what you may have read elsewhere, the dynamic range of this application, when properly deployed, is far beyond the capabilities of wide-band FM radio.
The following settings can be optionally used in a USB radio interface context in "[[Usbradio.conf|/etc/asterisk/usbradio.conf]]". If these keyword and value pairs are not present, their values default to zero (0). These alternate filters should be used with care. Note that additional computing power and radio adjustments may be necessary depending on your application. They have been extensively tested and work fine even with the Raspberry Pi3. Unlike other distributions, we encourage the use of the usbradio channel driver (chan_usbradio), or what we commonly call "Full DSP" in AllStarLink 1.01. This feature will also work in simpleusb, if that's what you prefer.
This feature is immediately available in new AllStarLink installations and updates.
This feature is immediately available in new AllStarLink installations and updates.
Receiver Audio Low Pass Filter Options:
=== Receiver Audio Low Pass Filter Options: ===
* rxlpf=0; 3.0 kHz cutoff. Default value for reduced noise and increased intelligibility.
* rxlpf=0; 3.0 kHz cutoff. Default value for reduced noise and increased intelligibility.
* rxlpf=1; 3.3 kHz cutoff for increased high end, sibilance, and brightness.
* rxlpf=1; 3.3 kHz cutoff for increased high end, sibilance, and brightness.
* rxlpf=2; 3.5 kHz cutoff for even more high end, sibilance, and brightness.
* rxlpf=2; 3.5 kHz cutoff for even more high end, sibilance, and brightness.
Receiver Audio High Pass Filter Options:
=== Receiver Audio High Pass Filter Options: ===
* rxhpf=0; 300 Hz cutoff. Default value to reduce sub-audible signals for retransmission, and also in the receiver speaker.
* rxhpf=0; 300 Hz cutoff. Default value to reduce sub-audible signals for retransmission, and also in the receiver speaker.
* rxhpf=1; 250 Hz cutoff for additional received and retransmitted bass response. We recommend using this filter with a CTCSS tone no higher than 186.2 Hz.
* rxhpf=1; 250 Hz cutoff for additional received and retransmitted bass response. We recommend using this filter with a CTCSS tone no higher than 186.2 Hz.
Transmitter Audio Low Pass Filter Options:
=== Transmitter Audio Low Pass Filter Options: ===
* txlpf=0; 3.0 kHz cutoff. Default value.
* txlpf=0; 3.0 kHz cutoff. Default value.
* txlpf=1; 3.3 kHz cutoff for increased high end, sibilance and brightness.
* txlpf=1; 3.3 kHz cutoff for increased high end, sibilance and brightness.
Transmitter Audio High Pass Filter Options:
=== Transmitter Audio High Pass Filter Options: ===
* txhpf=0; 300 Hz cutoff. Default value to reduce interference between voice and sub-audible signaling tones and codes.
* txhpf=0; 300 Hz cutoff. Default value to reduce interference between voice and sub-audible signaling tones and codes.
* txhpf=1; 250 Hz cutoff for increased bass response in transmitted audio.
* txhpf=1; 250 Hz cutoff for increased bass response in transmitted audio.