Message-ID: <595FB81A.5090606@posteo.de>
Date: Fri, 07 Jul 2017 18:34:34 +0200
From: DK7FC <selberdenken@posteo.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <15ca21dc75e-1e15-bcda@webprd-m105.mail.aol.com> <0f9558b4-457d-a395-58c9-7f9be3393cdd@sky.com> <4767d79f-2bf6-d838-bfd4-3e78102d6f5d@abelian.org> <510c15eb-b57a-0ebb-9037-1f83e0652cf2@sky.com> <933fcc32-d4c9-10cd-14b4-c179d66e27f9@abelian.org> <7ab80e0f-40d7-6b07-19c1-f4b256d47c52@sky.com> <a9c1a7cc-d835-fb85-1ae4-1682303d0c39@abelian.org> <594DB217.8060707@posteo.de> <2eb826d6-d299-7b37-cf64-f5bef6718f24@abelian.org> <e1b35334-bee0-19e3-c923-e448181ef608@abelian.org> <595E4420.7060405@posteo.de> <alpine.DEB.2.11.1707061915380.714@mailn.lipkowski.org> <ac5cf362-22db-d073-23ce-88a0d454a37b@abelian.org>
In-Reply-To: <ac5cf362-22db-d073-23ce-88a0d454a37b@abelian.org>
Subject: Re: LF: Octo-soundcard for the Raspi, another question
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: RO

Hi Paul,

Am 06.07.2017 20:13, schrieb Paul Nicholson:
> > channel 1 seems to show some minor glitches, see attachment.
>
> Looks bad.   Run the signal through vtstat -i to see
> if channel one is clipping at all.
>
>   vtread ... | vtstat -i
>
> Maybe both channels are close to hitting 1.0 amplitude in
> the stream and ch1 is slightly higher gain.  You need to
> look out for clipping if using integer sample formats.

-First checked the signal with vtread | vtstat -i and got:
format: float8
channels: 2
samples: 3006464
clips: 0
breaks: 0
sample rate: 24000, correction 1.00000000
duration: 125.2693333 seconds
start: 2017-07-05_03:19:11.000000
end: 2017-07-05_03:21:16.269333, interval 125.2693333 seconds
mean,rms,peak: 1 4.538e-03,5.045e-03,7.630e-03
mean,rms,peak: 2 4.507e-03,5.010e-03,7.691e-03
----
...so this looks fine, as expected.

-Next i took the original audio interface delivered together with the 
card (not my homemade 3 channel BNC input interface). Repeated the test, 
got the same  (bad) effect on CH1.
-Next i run the vt processes from the console (not from the script) just 
to see if there are differences: No difference, the same effect.
-Next i recorded a file without vttime and without vtresample. Converted 
to wav, displayed in SpecLab: Still the same effect!
-Next i made a wav file from CH2 and CH3, just to see how CH3 looks in a 
spectrogram, when injecting the same 500 Hz signal: CH3 looks better 
than CH1 but some minor glitches are still there.

Well, we're discussing about signals of > 60 dB SNR. Will this cause a 
significant performance reduction at all? Did you do similar large 
signal tests as well and observed the results?
Should i ignore these faint effects? Maybe it is more useful to finally 
connect two antennas and record a first VLF signal with some natural 
noise in the background...

73, Stefan