[GreenKeys] ITTY/RTTY Sampling tests

[Paul Heller]

Interesting. And I was a bit incorrect in my previous statement. 

I have been sampling at 16 bits per sample and dropped the transmission from 16 to 8.  If I drop the sampling to 8 bits per sample (sampling and transmission both 8) and the rate to 8kHz I get an empty stream (no audio). Remember it is an mp3 stream, so I’m guessing there is compression.

I need to make a table, but sadly it won’t display well with this email font. So here is a picture of it:




Paul



> On Sep 23, 2021, at 8:13 PM, ad7i <ad7i at ad7i.net> wrote:
> 
> With the 8K sampling, how many bits per sample were used per sample?  
> 
> The reason I ask is because the 1970s T1 systems did sample at 8000 sps and transmitted 8 bits per sample, but those 8 bits represented a compressed (compandered) value.  Although I've forgotten the specifics, the entry on Wikipedia for uLaw coding seems to indicate that the compander transformed the data from 14 bits uncompressed to 8 bits compressed, and vice versa at the RX end.
> 
> Paul, ad7i
> 
> 
> On Thu, Sep 23, 2021 at 8:54 PM Paul Heller <phearvada at gmail.com> wrote:
> It was definitely sampled at 8K. As I said, sampling at 11K and 22K were fine. It only dropped when sampling at 8K. 
> 
> The streaming software does not know about sample rates - it just sends it out.
> 
> It’s a puzzle
> 
> Paul
> 
> > On Sep 23, 2021, at 6:04 PM, Harold Hallikainen <harold at w6iwi.org> wrote:
> > 
> > I don't know what the combination of hardware and software is, but is it
> > possible that the audio was being sampled at a higher rate than 8k, then
> > being streamed at 8k? This would explain the frequency drop and bit rate
> > drop. But, it seems like the transmit buffer would eventually overflow.
> > 
> > Harold
> > 
> > 
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