CD quality? At 22kHz sampling? No.
(09-09-2017, 01:30 PM)Cardigan Wrote: [ -> ]CD quality? At 22kHz sampling? No.
That's only because the MP3 example file they're using has that sample rate.
Other vaiants of the same code use the embedded sample rate, so 44.1 etc. are achievable, e.g. look at the RDS-enabled version... the internal rate is 228 kHz, so the input file is upsampled.
https://github.com/ChristopheJacquet/PiFmRds
To get hung up on the exact details of the audio quality is somewhat missing the point
Naturally, whatever the source, no FM broadcast will ever be CD quality given that it stops at 15kHz and will never have the noise floor of 16 bit audio. But against that, how many commercially produced CDs take full advantage of the potential of 16 bit audio? Even before the advent of the "loudness wars", 16/44.1 is over-engineered for delivery to the home, and 24/192 is marketing BS.
Anyway, something to try next time I'm messing with a Pi
(10-09-2017, 09:38 AM)Mark Hennessy Wrote: [ -> ]Anyway, something to try next time I'm messing with a Pi
Indeed - I love left-field ideas - I'll probably never use it, but what mad train of thought led to this? A heavy night in the pub, methinks... and then someone adds RDS to it!
The 15kHz FM BW is also often missed, though many modern CD players are full 16 bit.
Never tried a Pi, maybe one day I'll play about with one and see how I get on.
(10-09-2017, 10:38 AM)Murphyv310 Wrote: [ -> ]Never tried a Pi, maybe one day I'll play about with one and see how I get on.
You need an objective - a project - else you'll just faff about and get nowhere...
I use about 10 now - 6 are dedicated media players serving up music and radio around the house and outbuildings. the other are doing stuff like advert-stopping DNS servers (see the
Pi-Hole project) or CCTV control.
With the Pi 3, you get WiFi, BLE (Bluetooth Low Energy) and a world of support. You can use a BT keyboard and mouse and an HDMI monitor - then you're done.
If using them as media servers, you don't need screens/keyboard/mice, just a network connection.
Interesting Nick.
A few of my friends have said I'd find them great for projects, I can see they indeed would be. Maybe get one for Christmas.
(10-09-2017, 09:04 AM)Nick Wrote: [ -> ] (09-09-2017, 01:30 PM)Cardigan Wrote: [ -> ]CD quality? At 22kHz sampling? No.
That's only because the MP3 example file they're using has that sample rate.
Other vaiants of the same code use the embedded sample rate, so 44.1 etc. are achievable, e.g. look at the RDS-enabled version... the internal rate is 228 kHz, so the input file is upsampled.
https://github.com/ChristopheJacquet/PiFmRds
What's wrong with
analogue design? What's next - "use your Raspberry Pi as a tin opener"?
As regards FM bandwidth; we often see the BBC spec of 15kHz bandwidth quoted, but how many dB down is it at that point? What sort of filtering is used, any phase EQ, turnover frequency, all that?
(11-09-2017, 10:36 AM)Cardigan Wrote: [ -> ]As regards FM bandwidth; we often see the BBC spec of 15kHz bandwidth quoted, but how many dB down is it at that point? What sort of filtering is used, any phase EQ, turnover frequency, all that?
Analog is hard, but so is high-speed digital (which has many of the same issues as analog).
Of course you can use a fully analogue design, the point here is that it's a left field crazy idea that just happened to work...
Others then enhanced it for fun, adding RDS, pre-emphasis. DMA etc.
Just a bit of fun and lateral thinking...
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