- September 27, 2017 at 3:01 pm #11397Carl BlareParticipant
Total posts : 1540
Sending one audio chain to three different kinds of transmitter poses challenges for the audio bandwidth.
FM transmitters handle the widest audio bandwidth with a response of 20 to 15 kHz (the high frequencies are rolled off above 15 kHz to avoid collision with the 19 kHz stereo pilot frequency but mono FM allows unlimited high frequency response).
AM transmitters face a channel width of 10 kHz but the audio pass is only 50% of this because both positive and negative swings of a 5 kHz signal add up to 10 kHz. Don’t be confused, I believe with NRSC pre-emphasis sone stations are allowed to occupy 20kHz for a total audio response of 10kHz on a wide-band radio receiver.
Streamitters (Internet Radio Stream Servers) are a whole other breed with audio quality governed by bit and sample rates, which may or may not comply with AM FM audio bandwidths.
This whole ball of mess came to KDX Worldround Radio based on two recent experiences:
Wearing a DXer hat we tuned around the AM dial to observe which stations splashed into adjacent channels, suggesting wide-bandwidth transmission, and came upon one that was so tightly confined to its channel that I was able to hear a far off station on an adjacent channel without any splashover from the local. I was impressed and set my audio bandwidth to exactly 5 kHz and being a voice talk radio station it sounded alright on our FM channel as well.
No doubt music stations need as wide an audio band pass as they can get, but we carry little music.
Complications arose the day KDX decided to serve the most under-served audience in the world, a growing population suffering under slow internet service brought on by the skyrocket costs and inadequate service outside of major cities also to mention slow computers and a reviving interest in dial-up modems.
Enter KDX ONLINE 8 kbps 8 kHz.
At first we experienced heavy crackling ond poping because such low stream rates cannot transpose the upper part of the audio band, but some careful tweaking inside Stereo Tools Audio Processing software has somehow smoothed everything to the point where it all works.
If things work don’t do anything else.September 27, 2017 at 5:26 pm #55650Carl BlareGuest
Total posts : 45366
Now that KDX Worldround has achieved audio band pass settings suitable for our transmitters, we look now at the physical air space between the loudspeaker and the listener’s ears.
We assume that environments are noisy, whether indoors, outdoors, or in the car.
What speech frequencies in the audio spectrum are most effective at delivering intelligible voices? That is a science with researchable documentation.
It’s very nice when your audio sounds good in the peace and quiet of the control room, but if you take a portable outside and try to hear the news from 10-feet away while trimming shrubbery, can you make any sense out of it?
Turning the volume up causes most portables to distort and the batteries to run down, so we maintain that a tailored EQ (equalized) spectrum shaping will make those voices cut through the air.
No need to get up, I’ll let myself out.September 28, 2017 at 12:14 am #55652MarkGuest
Total posts : 45366
Carl said”FM transmitters handle the widest audio bandwidth with a response of 20 to 15 kHz (the high frequencies are rolled off above 15 kHz to avoid collision with the 19 kHz stereo pilot frequency but mono FM allows unlimited high frequency response).”
So true, The Decade MS-100 gives the stereo version 20HZ to 15KHZ but the mono version which I use 20HZ to 20KHZ.
Besides all recievers being more sensitive in mono the fidelity is better in mono also.
According to audiologists when you get your hearing tested they are concerned with speech and test you from 500HZ to 8KHZ, but are really only concerned with 6KHZ.
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