I seem to have missed out some of the posts including David's but yes I
need to process audio at 192 kHz. I have no desire to actually store
any audio at 192 kHz but I understand RD does not convert between
sample rates. The reason is as Fred points out, FM MPX has a bandwidth
of 56 kHz including RDS subcarrier so you have to sample at at least
twice that (Nyquist!) to be able to produce the full spectrum needed. I
could of course use 112 kHz but I suspect that would be even more
problematic to get working given 192 kHz is a fairly standard sample rate.
You've answered my question though - RD does not run at 192 kHz. I have
noticed high caed usage at 48 kHz so can imagine it'd be worse at higher
rates (although it's a little better with the pr43 debian packages which
include a fix for high CPU usage in caed (44% to 30%)).
What I cannot fathom is why RD is trying to connect to the jack server
and the ALSA interface... It connects ALSA to rd0 and then connects the
running jack instance to rd1. Is there any way to just to have it use
ALSA and not jack?
I wanted to avoid two cards because I want to take a microphone input
and mix it all on one jack instance which I can do with my current set
up reasonably well. But I may end up doing it anyway to provide the
ability to monitor 'off air'. This would be trivial if I had a couple
of clockable cards but I don't, I have some prosumer interfaces only.
Aaron
On 25/09/2015 17:29, Frederick Gleason wrote:
On Sep 25, 2015, at 09:56 31, David Klann <[email protected]> wrote:
Which brings up the point from Aaron's original point claiming to need
to encode the audio at 192KHz. Aaron, why is it that you think you
need this high of a sample rate? 48KHz is better than CD quality which
has always been better than FM quality. Are you confusing sample rate
with compression bit-rate?
AFAICT, he’s wanting to use StereoTool to generate MPX composite, which does
require 192 ksample/sec because of the ultrasonic spectral components involved
(up to around 48 kHz baseband, more if the RDS encoder feature is also used).
Those who have been around here for awhile may remember Dan Mills, who was one
of (might have even been *the* first) original developers of this concept.
IIRC, his setup involved two sound cards, each bound to a separate instance of
JACK (one operating at 48 ksamples/sec for Rivendell, and another at 192
ksample/sec for the MPX generation), along with appropriate sample clock
interconnection to keep both cards operating in sync. His processor talked to
*both* JACK graphs. The trick as I recall was getting the two cards to clock
at a precise 4:1 ratio. Not a trivial setup. I suppose you could do something
similar, using JACK’s ‘dummy’ backend for the Rivendell graph, but the devil
will be in getting the clocks to sync.
Cheers!
|----------------------------------------------------------------------|
| Frederick F. Gleason, Jr. | Chief Developer |
| | Paravel Systems |
|----------------------------------------------------------------------|
| A room without books is like a body without a soul. |
| -- Cicero |
|----------------------------------------------------------------------|
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Kind regards
Aaron Horn
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