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Wednesday, March 20, 2013

Podcast Noise Explained; Mic advice from Germany


Hello Bill,

This might be down the drain for you, but I only listen to your podcast very few months:

The background hiss you mentioned in Soldersmoke 148 definitely was a crosstalk from the switching voltage converters for the CPU in your laptop. The CPUs these days are operated with voltages in the .7 V to  2 V range,with currents from several Amperes up. A high-performance CPU may dissipate150 W which can easily mean supply currents of 100 A an more. The CPU operating voltage, especially in a laptop, might change several 100 times a second. I think you can imagine the rest.

Why is that voltage adaption so important? This is within your domain: The biggest heat source in digital electronics these days is charging and discharging capacitors. Unless you use a resonant circuit (which you cannot do on a chip) you dissipate P = 1/2 C U^2 with every discharge. Yes: Power depends on the square of the supply voltage. And at a clock frequency in the 2 GHz range you charge and discharge all those capacitors quite often. Each of these has a capacity in the fF (.001 pF) range, but you have billions of these...

Over the time you had quite some complaints about your whistling s. In former times this was definitely made worse by some technical problems. But this is a problem long gone. An Soldersmoke 149 I believe the remaining problem simply was the tooth gap you described a few years back.


BTW: You could easily reduce the file sizes of your podcasts by at least 50% with a few simple measures:

- You should record the podcast as you do now, with a 44 or 48 kHz sampling rate, that's fine. I would even record in wave format.

- Afterwards downsample your recording to a sampling rate of 12 or 16 kHz. This provides ample audio bandwidth for this purpose. See e.g.
http://forum.audacityteam.org/viewtopic.php?f=28&t=19705

- Then create the MP3 file with a signal rate of 48 or 64 kbit/s.


BTW: Last weekend at a ham flea market I got a variable transformer. Now I can try to revitalize my Drake TR4C that has not seen any electricity for some 30 years. I bought it when I got my shortwave license in 1975. At that time I lived with my parents. Then I could operate it during my military service. But after that I got an electronics engineer and lost all possibilities to erect any kind of SW antenna. Only three years ago I got my own house near Munich. But I'm hardly at home and I nearly exclusively operate from my car. I will not try this with any kind of boatanchor :-)

vy 73
Alexander
DL4NO

------------------------------------
Von: solder smoke [mailto:soldersmoke@yahoo.com]
Gesendet: Dienstag, 19. März 2013 09:49
An: DL4NOAlexander
Betreff: Re: Soldersmoke 148: Background Hiss



Thank you Alexander.  That is very useful information.   I have switched to a new computer and I think the hiss  problem is gone.   The gap in my teeth remains however! 

 

I am thinking about getting a better microphone.  Any advice on this?

 

I am glad to  hear that you are back into ham radio.  My Elmer (the guy who helped me get started as a novice) was an immigrant from Germany (Hilmar,  WN2NEC).  He was an excellent technician.   I still use some of the things he made for me.

 

73  Bill
------------------------------------------------
Hello Bill,
 
about a microphone: Think about a headset, possibly a wireless one. I would search forums about dictation software for advice.
 
A headset fixes the position of the microphone relative to your mouth. At the same time the microphone is near your mouth so any ambient noise is suppressed. A wireless [Bluetooth] headset would allow you to move around freely. Unless you come near a larger hard or soft surface or leave the room the sound should not change much. You could arrange the materials for your next podcast around the room and move from "chapter" to "chapter". And as the digitizing happens in the headset all weak analog signals are safe away from any voltage converters and digital electronics.
 
I had never left ham radio, I just reduced and modified my activities. 2m or 70cm FM were always possible. Here in Germany we have more than 1,000 repeaters. Many of these repeaters have Echolink capabilities. For the last 15 years I have more or less exclusively worked from my car while driving. In my car I have a FT-857D. For shortwave I use monoband antennas on a PL mount at on the roof of my car. For pictures see http://www.dl4no.de/thema/amateur1.htm. The schematic in http://www.dl4no.de/thema/mobil-st.htm shows how I ensure that my TRX gets its 22 A peak from the 12V outlet in the trunk of my car: I buffer it with a 1 F capacitor - really 1,000,000 µF! The mean supply current during SSB transmit is less than 5 A.
 
A quite important role in my ham life play the local chapters of our German ham radio society DARC. There are more than 1,000 of them, each with its own DOK. So wherever my customers are, at least one local ham meeting a month is not far away. I participate in their activities, give a lecture from time to time. This is a big help as I mostly work at my customers and these are scattered all over southern Germany.
 
Just a short story with some local connection for you: Peter, DL5NC, spent quite a few years in the Washington, DC area. He has a US call, but please don't ask. He was born some 50 km from my home town. Formally this area, Franconia, has been part of Bavaria since 1806. Nevertheless we believe that the Bavarians have no clue how to brew beer.
 
One Friday morning (your time) he was on his way into Washington, DC. Through Echolink he connected to a Munich repeater while I was in the afternoon rush hour on my way to a beer garden. I told him that this was one of the few places in Munich where you could get a decent beer. And otherwise I had my own beer at home imported from Franconia. He threatened to never again talk to me because of mental cruelty. In the meantime he returned to Germany and got a neighbor. We drank a few Franconican beers together in the meantime :-)
vy 73
Alexander
DL4NO
 


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1 comment:

  1. Composer/Musician point of view: fascinating and useful is the technical "porqué" of it all...but ultimately...those fine filters we have twixt the ears make us hear what we are wont to hear. Content counts. Saluti DAL Messico...XE1GXG

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