Changes

= Audio Filters =

= 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 release of PTTLink 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.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 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.  

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 PTTLink 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 PTTLink installations and updates.  

=== Receiver Audio Low Pass Filter Options: ===

=== Receiver Audio Low Pass Filter Options: ===

Here's a brief synopsis of what the frequency response from Rx to Tx is like with the DEFAULT (zero) filters that everybody is currently using   

Here's a brief synopsis of what the frequency response from Rx to Tx is like with the DEFAULT (zero) filters that everybody is currently using   

<gallery heights="300px" widths="300px">

<gallery heights="300px" widths="300px">

AllStarLink Filter 1.png

Ptt filter 2.png

</gallery>

</gallery>

<gallery heights="300px" widths="300px">

<gallery heights="300px" widths="300px">

AllStarLink Filter 2.png

Ptt filter 1.png

</gallery>

</gallery>

In summary, we believe if you switch all of the filters to 1 you'll be very happy with the improvement in quality and no further tweaking will be necessary.  Our goal was to make the "1" filters - plug and play.  The improvement will obviously be greatest when both the repeater you're on as well as the repeater of the user(s) you're talking to have the updated filter code, and have taken advantage of these filters.

In summary, we believe if you switch all of the filters to 1 you'll be very happy with the improvement in quality and no further tweaking will be necessary.  Our goal was to make the "1" filters - plug and play.  The improvement will obviously be greatest when both the repeater you're on as well as the repeater of the user(s) you're talking to have the updated filter code, and have taken advantage of these filters.