[arm-allstar] Audio processing, was Re: cdm1250 transmit audio

Patrick Perdue borrisinabox at gmail.com
Tue Mar 3 04:39:50 EST 2020 

I'm mostly trying to fill out the bottom end from radio TX audio more 
than increasing the top. I realize attempting to increase high end 
response from RF to ASL would be generally pointless due to FM bandwidth 
restrictions, niquist theorem, 3.5 k brick wall low pass filter, etc. 
But, if I can extend the bottom just a little past where the filters 
live, all without going into distortion and saturation, or getting into 
frequencies around where PL tones live, even just 10 or 20 hz makes a 
pretty significant difference with some radios, and not at all with 
others. Listening to my radios on simplex vs unfiltered through my SM50 
from the other side of Allstar, this can be achieved, but I admit that I 
am picky about audio. I have processes for maximizing intelligibility of 
digital modes as well. And, of course, every time I hear an Allstar node 
where GSM is the preferred codec, I die a little inside.

On 3/3/2020 1:35 AM, "Doug Crompton via ARM-allstar" wrote:
> Patrick,
>
>   I really don't have time to play audio games. The audio that Allstar
> provides is about the best voip out there period. If you are using DMR or
> digital modes I don't see why you would have any complaints about Allstar.
> The human voice has little content above 3Khz hence most radios use that as
> a high end. SSB filters are usually less than 3Khz, sometimes as low as
> 2Khz with good intelligibility. I really think you should spend your time
> on something more useful. All radios are different and if you are using a
> handheld with a 2" (or less) speaker what can you expect. As I said in my
> prior email the radios tailor the audio to a great extent and that is
> beyond our control. If I was complaining about audio I would say the low
> end suffers more than the high end but that is mainly because of filtering
> for PL and also the size of the speakers in most radios. Take a radioless
> node at both ends and put it on a good size speaker turn off PL filtering
> and it will blow your socks off with fidelity.
>
>
> *73 Doug*
>
> *WA3DSP*
>
> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
>
>
> On Tue, Mar 3, 2020 at 12:28 AM "Patrick Perdue via ARM-allstar" <
> arm-allstar at hamvoip.org> wrote:
>
>> The entire system runs at 8 kHz sampling rate. Even if the rate was
>> increased, there is filtering happening in app.rpt. Doug could give you
>> more details about exactly how that low pass filter works.
>>
>> As you're going through two radios to get to the network, if you're not
>> using a radio-less node or something like iaxrpt, which has it's own
>> non-defeatable high pass filter, each of those radios will apply their
>> own characteristics.
>>
>> Using the G7RPG microhub and it's Baofeng node vs. my Motorola SM50, I
>> can say that the Motorola does let some more highs through in both
>> directions, but not all that much, even on simplex when monitored
>> through discriminator output with an SDR. It is definitely better on the
>> low end for both receiving and transmitting, and has a much, much lower
>> noise floor on the audio path. Re the Motorola, I wish I could turn off
>> all the software filtering of SimpleUSB, notch out my PL tone frequency,
>> and let it roar, but when I tried that, DTMF detection totally failed.
>> Just using an old Wouxun HT, people did notice a difference when I took
>> the PL filter away, especially those with good speakers, but most people
>> probably wouldn't care.
>>
>> I have also plugged an Alinco EMS-57 clone microphone into my URI,
>> unfortunately without the added op-amp of the URI or another preamp to
>> get it closer to line level, so I had to turn RXBoost on and menu 2 to
>> 999 just to be heard, and the mic doesn't sound that great anyway, but
>> you do get the idea that it's a fuller sound.
>>
>> I'd like to use a better mic and some processing, but that's a project
>> for when I actually have a permanent place to live, I.E. not now.
>>
>>
>> On 3/2/2020 7:18 PM, "Chris Smart via ARM-allstar" wrote:
>>
>>> I have a much more basic audio question.
>>>
>>> what in an Allstar node chops things off around 3K? Is it the Baofeng
>> radio module in most nodes, or is it something to do withthe fact that
>> we're using pbx sofftware, so it treats everything as telephone audio?
>>>
>>>
>>> Sent from Chris's iPhone.
>>>
>>>
>>>> On Mar 2, 2020, at 16:51, Patrick Perdue via ARM-allstar <
>> arm-allstar at hamvoip.org> wrote:
>>>> I've gotten quite good results using hardware vocoders. DMR is far
>> more robust than many give it credit for, especially if you don't use the
>> software md380-emu implementation. Even some background is tolerated, which
>> is pretty awesome when you consider the limited bandwidth and complexity of
>> the DV modes. I'm always interested in improving audio wherever it can be
>> improved, however.
>>>>
>>>>> On 3/2/2020 3:12 PM, "Doug Crompton via ARM-allstar" wrote:
>>>>> Patrick,
>>>>>
>>>>>    First of all this is probably not happening soon. There are many
>> other
>>>>> more important things on the list. Also it is almost impossible to
>> improve
>>>>> something like crappy digital audio. If there was it would already be
>> done.
>>>>> My suggestion is don't use it! But many people put up with it as they
>> think
>>>>> it is some kind of advance in technology. Funny what you can seel
>> people!
>>>>>
>>>>> *73 Doug*
>>>>>
>>>>> *WA3DSP*
>>>>>
>>>>> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
>>>>>
>>>>> On Mon, Mar 2, 2020 at 3:01 PM "Patrick Perdue via ARM-allstar" <
>>>>> arm-allstar at hamvoip.org> wrote:
>>>>>
>>>>>> I'm definitely looking forward to any future audio processing support,
>>>>>> especially if SoX is involved, since we could then use ladspa. I would
>>>>>> especially like to process analog input to clean things up for digital
>>>>>> bridges. I'm thinking downward expander plus gate, so the digital
>>>>>> vocoders have less noise to process, especially with strong to
>> moderate
>>>>>> analog signals, EQ and limiter. This could also help with the ever
>>>>>> present echo link 8-bit dithering. This is something I've wanted to do
>>>>>> for a while. Having a moderate downward expander and EQ or light
>>>>>> multi-band compression on my transmitted audio to Allstar would be
>> nice
>>>>>> as well. Just something subtle to keep levels and equalization in line
>>>>>> between radios, but not to be obvious that there is processing.
>>>>>>
>>>>>>
>>>>>> On 3/1/2020 10:23 PM, "Doug Crompton via ARM-allstar" wrote:
>>>>>>> Jed,
>>>>>>>
>>>>>>>     Pre and de-emphasis are not meant to be used when they are
>> applied to
>>>>>> the
>>>>>>> audio to/from the transceiver. Using them to make things sound more
>> or
>>>>>> less
>>>>>>> bright when they have already been applied is not a good idea
>> especially
>>>>>> on
>>>>>>> audio going out to the network. Pre-emphasis increases the high end
>> at a
>>>>>>> prescribed rate for audio FROM your node, what you hear. De-emphasis
>>>>>>> decreases high end on audio TO your node, what others hear.  Most of
>> us
>>>>>> are
>>>>>>> using radios that do this internally and leave these settings OFF.
>> If you
>>>>>>> were using a radio that did not apply one or the other or both you
>> would
>>>>>>> turn the appropriate one on. The bottom line is that they are not
>> meant
>>>>>> for
>>>>>>> casual audio equalization but rather for a defined method every FM
>> signal
>>>>>>> uses.
>>>>>>>
>>>>>>> It is in our plans and sometime in the future you will be able to
>> apply
>>>>>>> software equalization using an external program such as sox but for
>> ow if
>>>>>>> you must change equalization your best bet is feeding the analog
>> audio
>>>>>> out
>>>>>>> of the FOB through a hardware equalizer.
>>>>>>>
>>>>>>>
>>>>>>> *73 Doug*
>>>>>>>
>>>>>>> *WA3DSP*
>>>>>>>
>>>>>>> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio
>>> *
>>>>>>>
>>>>>>> On Sun, Mar 1, 2020 at 5:00 PM "Jed Barton via ARM-allstar" <
>>>>>>> arm-allstar at hamvoip.org> wrote:
>>>>>>>
>>>>>>>> Hey guys,
>>>>>>>>
>>>>>>>> So i'm trying to do some audio adjustment on my cdm1250 to make it
>>>>>>>> sound better.  I'm trying to figure out the pre-emphasis and
>>>>>>>> deemphasis on the radio.  I wanna add a little more high end to the
>>>>>>>> transmit audio.  Can i try this in simple USB, or where should i go?
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>>
>>>>>>>> Jed
>>>>>>>> _______________________________________________
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