Massive Master
www.massivemastering.com
Didn't really know where to post this so I figured this was the best place.
So I'd imagine most here know that I'm a mastering guy. I'm also a long-time radio enthusiast with various band licenses going all the way back to the 11m Citizen's Band back when you needed a license for that band. Recently passed the FCC amateur radio "General" class exam, which I'm pretty happy about.
As one would probably figure, my mastering room is also my "radio shack" (that's where the place got the name). I'm not using "serious" power in here -- Mostly only on 2m and 70cm frequencies with maybe 15-25w of Tx power. Now that I've passed the General and I can work on HF, that might change soon. But that's not the subject. ANYWAY ---
One thing I do rather frequently here (and shame on you if you don't) is calibrate - or simply confirm calibration of the system. Various sines / sweeps and what not through the chain making sure the noise floor is where it's expected to be and that L/R match to within ridiculously picky specs.
With the radio stuff in the room, I occasionally transmit at various frequencies and various power levels to see how a "silent" chain will react -- Usually a HT (handy-talkie, what most would call a walkie-talkie) at maybe 5w PEP, wandering around the room and looking at the meters to see how much RFI (radio frequency interference) sneaks into the chain. It's not much - But there's no doubt, when I'm working on something in here, I'm not transmitting. You can see it on the meters when I key up. It's not the fault of the (otherwise ridiculously quiet) chain - It's just a fair amount of EMI/RFI at very close proximity to the gear. I totally expect that there is going to be some amount of radiation that affects the integrity of the audio signal to a small extent. And although it would be totally buried by a super-quiet audio signal, I wouldn't want it on *my* album, so I'm certainly not going to subject yours to it.
To that end, part of my calibration "suite of tools" is a software defined radio (SDR) that presents me with a waterfall spectrum analysis of various frequencies. Originally (and usually), I just used it to listen to frequencies I didn't have transmit privileges on. But I quickly found out that it was a very handy tool to find sources of RFI/EMI that could leak its way into the system. You can't fix what you don't know about - and if you need a ferrite choke that works at a particular frequency because a washing machine next door or a nifty lamp in the next room is creating interference in your chain (true story), you need to know what frequencies you need to filter out. You'd probably be shocked (no pun intended) at the amount of electromagnetic interference that might be occurring in your space from things like LED lights and video monitors.
So last week, I was tuning in to a specific 2m repeater for a "net" (that's basically a group of radio users who check in to a net controller who "conducts" traffic from there) on 146.470 MHz and found the band to be "stomped on" -- It seemed as if someone was keyed up, transmitting an otherwise silent signal (a FM carrier with no modulation), which was being transmitted from this repeater around 35 miles away. This wasn't the first time I caught this anomaly on this particular repeater and I figured it was long sessions of some form of digital communications going on. This time however, I knew there was supposed to be a particular net. Being FB friends with one of the people who I figured would also be on, I said "Hey - what's going on? Someone is Tx'ing silence? Been there for 30 minutes" and she replied "??? The net is going. I'm surprised you haven't checked in yet."
SOOOOOoooo -- Loaded the SDR on to the main audio machine (it's a "dongle" receiver with a remote dipole antenna that connects via a support program) to find out where this interference was coming from and POOF - It disappeared. Dammit, foiled. Everything was fine, checked in to the net, all was wonderful. Until the next day when it happened again...
Loaded the SDR and POOF - It disappeared. Again. Okay, now I'm wondering WTF is going on here. Watched my 2m receiver and rebooted the computer. Rx (receive) indicator lit up (again, strong carrier and no modulation) and then went out as I saw the audio meters playing the "Windows" sound. Then it lit back up again. So I loaded an audio file into WinAMP or what not and POOF - It disappeared.
THAT RF RADIATION IS COMING FROM MY AUDIO COMPUTER.
Did just a whisker of experimentation and had 5 or 6 people on a different repeater throwing theories and suggestions at me. Booted again, saw the signal again, Windows sound no signal, then back again. Figured maybe it's a drive or something so I decided to start unplugging things to see if I could make it disappear. First thing I could reach was my USB to AES interface.
One shot / one kill. Signal immediately gone. Rebooted again to get the signal back and *power cycled* the interface. Gone again and stayed gone. Repeated this a few times to make sure there were no anomalies and I was "in charge" of the situation.
So on the "good news" side, this signal, that I never would've known about otherwise, has NOT affected the audio quality in the system. As soon as the device is "in use" by playing audio, the interference stops. But lemme tell you something - To "full quiet" a signal from a fairly powerful repeater takes a little Tx power. So to find out what I was dealing with, I hooked my SDR up to a laptop, rebooted and saw this relatively scary sight:
That is a BIG F'ing peak at 146.763 MHz. (the display shows 146.764 - long story) which was totally overtaking the signal that I was receiving at 146.760. There were others in the 136 MHz range and I assume plenty of other harmonics that I didn't have time to track down (takes a reboot of the computer and then a reboot of the device to confirm).
Next step at this point is to get another HAM buddy with a directional wattmeter out here to find out if that's a "dangerous" amount of RF radiation. When I'm using certain (usually really cheap, Chinese mfg'd) radios, I can feel the heat in my face during long conversations. I don't *think* I feel anything like that with this, but this device is a few feet away. Still, that's a pretty darn strong signal. Especially for something that shouldn't be transmitting anything at all.
I've contacted the manufacturer - FTR, we're talking about a MiniDSP U-DIO8 here - about the situation and they seem to be open to trying a few things because they can't replicate the situation there (I have to wonder if they have a SDR lying around, but maybe they do). And also FTR, the SDR in question is the RTL SDR USB with the RTL dipole antenna. If you don't have one, you probably should. It's a blast to listen to broadcasts and transmissions from all over the world that are passing through you anyway (RF is non-ionizing radiation, so it's not turning you into a monster or anything) and it's absolutely a wonderful tool for finding miscellaneous sources of RFI/EMI in your studio.
So I'd imagine most here know that I'm a mastering guy. I'm also a long-time radio enthusiast with various band licenses going all the way back to the 11m Citizen's Band back when you needed a license for that band. Recently passed the FCC amateur radio "General" class exam, which I'm pretty happy about.
As one would probably figure, my mastering room is also my "radio shack" (that's where the place got the name). I'm not using "serious" power in here -- Mostly only on 2m and 70cm frequencies with maybe 15-25w of Tx power. Now that I've passed the General and I can work on HF, that might change soon. But that's not the subject. ANYWAY ---
One thing I do rather frequently here (and shame on you if you don't) is calibrate - or simply confirm calibration of the system. Various sines / sweeps and what not through the chain making sure the noise floor is where it's expected to be and that L/R match to within ridiculously picky specs.
With the radio stuff in the room, I occasionally transmit at various frequencies and various power levels to see how a "silent" chain will react -- Usually a HT (handy-talkie, what most would call a walkie-talkie) at maybe 5w PEP, wandering around the room and looking at the meters to see how much RFI (radio frequency interference) sneaks into the chain. It's not much - But there's no doubt, when I'm working on something in here, I'm not transmitting. You can see it on the meters when I key up. It's not the fault of the (otherwise ridiculously quiet) chain - It's just a fair amount of EMI/RFI at very close proximity to the gear. I totally expect that there is going to be some amount of radiation that affects the integrity of the audio signal to a small extent. And although it would be totally buried by a super-quiet audio signal, I wouldn't want it on *my* album, so I'm certainly not going to subject yours to it.
To that end, part of my calibration "suite of tools" is a software defined radio (SDR) that presents me with a waterfall spectrum analysis of various frequencies. Originally (and usually), I just used it to listen to frequencies I didn't have transmit privileges on. But I quickly found out that it was a very handy tool to find sources of RFI/EMI that could leak its way into the system. You can't fix what you don't know about - and if you need a ferrite choke that works at a particular frequency because a washing machine next door or a nifty lamp in the next room is creating interference in your chain (true story), you need to know what frequencies you need to filter out. You'd probably be shocked (no pun intended) at the amount of electromagnetic interference that might be occurring in your space from things like LED lights and video monitors.
So last week, I was tuning in to a specific 2m repeater for a "net" (that's basically a group of radio users who check in to a net controller who "conducts" traffic from there) on 146.470 MHz and found the band to be "stomped on" -- It seemed as if someone was keyed up, transmitting an otherwise silent signal (a FM carrier with no modulation), which was being transmitted from this repeater around 35 miles away. This wasn't the first time I caught this anomaly on this particular repeater and I figured it was long sessions of some form of digital communications going on. This time however, I knew there was supposed to be a particular net. Being FB friends with one of the people who I figured would also be on, I said "Hey - what's going on? Someone is Tx'ing silence? Been there for 30 minutes" and she replied "??? The net is going. I'm surprised you haven't checked in yet."
SOOOOOoooo -- Loaded the SDR on to the main audio machine (it's a "dongle" receiver with a remote dipole antenna that connects via a support program) to find out where this interference was coming from and POOF - It disappeared. Dammit, foiled. Everything was fine, checked in to the net, all was wonderful. Until the next day when it happened again...
Loaded the SDR and POOF - It disappeared. Again. Okay, now I'm wondering WTF is going on here. Watched my 2m receiver and rebooted the computer. Rx (receive) indicator lit up (again, strong carrier and no modulation) and then went out as I saw the audio meters playing the "Windows" sound. Then it lit back up again. So I loaded an audio file into WinAMP or what not and POOF - It disappeared.
THAT RF RADIATION IS COMING FROM MY AUDIO COMPUTER.
Did just a whisker of experimentation and had 5 or 6 people on a different repeater throwing theories and suggestions at me. Booted again, saw the signal again, Windows sound no signal, then back again. Figured maybe it's a drive or something so I decided to start unplugging things to see if I could make it disappear. First thing I could reach was my USB to AES interface.
One shot / one kill. Signal immediately gone. Rebooted again to get the signal back and *power cycled* the interface. Gone again and stayed gone. Repeated this a few times to make sure there were no anomalies and I was "in charge" of the situation.
So on the "good news" side, this signal, that I never would've known about otherwise, has NOT affected the audio quality in the system. As soon as the device is "in use" by playing audio, the interference stops. But lemme tell you something - To "full quiet" a signal from a fairly powerful repeater takes a little Tx power. So to find out what I was dealing with, I hooked my SDR up to a laptop, rebooted and saw this relatively scary sight:
That is a BIG F'ing peak at 146.763 MHz. (the display shows 146.764 - long story) which was totally overtaking the signal that I was receiving at 146.760. There were others in the 136 MHz range and I assume plenty of other harmonics that I didn't have time to track down (takes a reboot of the computer and then a reboot of the device to confirm).
Next step at this point is to get another HAM buddy with a directional wattmeter out here to find out if that's a "dangerous" amount of RF radiation. When I'm using certain (usually really cheap, Chinese mfg'd) radios, I can feel the heat in my face during long conversations. I don't *think* I feel anything like that with this, but this device is a few feet away. Still, that's a pretty darn strong signal. Especially for something that shouldn't be transmitting anything at all.
I've contacted the manufacturer - FTR, we're talking about a MiniDSP U-DIO8 here - about the situation and they seem to be open to trying a few things because they can't replicate the situation there (I have to wonder if they have a SDR lying around, but maybe they do). And also FTR, the SDR in question is the RTL SDR USB with the RTL dipole antenna. If you don't have one, you probably should. It's a blast to listen to broadcasts and transmissions from all over the world that are passing through you anyway (RF is non-ionizing radiation, so it's not turning you into a monster or anything) and it's absolutely a wonderful tool for finding miscellaneous sources of RFI/EMI in your studio.