January
January 4
HAPPY NEW YEAR & THE 24-HOUR PHANTOM OF THE SURROUND CHANNELS
Greetings from the Lair, in 2008, no less! Egads, not only have I survived into the 21st century, but I'm starting to make inroads well into the new century!
I have just about completed migrating my "office" functions from a Windows 2000 PC to a newer Windows XP PC. Many complicated hardware and software installations were part of the process, as this PC controls scanners, the Kurzweil synths, a MIDI patch bay, FAX modem, and the MotU 896, to name the prominent items. A lot of software, ranging from page layout to OCR, to MIDI sequencing, to Office applications, to web publishing and some video editing applications reside on this system. A number of workarounds had to be... well, worked out. But it's 90% worked out and running smoothly.
The top story this time is something rather odd that happened on New Year's Eve and lasted 24 hours, almost to the minute. I'll relate the story as posted on an internet forum:
I built this system 32 years ago, and have regularly maintained and upgraded it over that span of time. The System consists of multiple amplifiers in a rack fed with 240vac, split 120vac for the low power equipment, which included preamps and electronic crossover networks.
I recently started using a spare Hafler 500 amp (one of two spares) for Surround Sound amplification, driven directly off the outputs of my DVD player's discreet 5.1 channel outputs. Speakers are floating and the amp outputs are not connected to any AC ground other than the speakers themselves. It has worked fine since last summer.
System was working normally the night of 12/31. Problem occurred 20 minutes into a movie, shortly before midnight.
Problem manifested as a loud popping noise, dominant in right surround channel, but heard in both surround channels, at about 6 cps—it sounded like a square wave. This blew the B+ fuse and the N-channel MOSFETs in the left channel of the surround sound amp, a Hafler 500, even though the popping issued from the right channel with greater amplitude.
After repair, amp works perfectly on bench. No oscillation, perfectly stable.
Reinstalled in rack, oscillation starts when left input is connected—even with connected equipment turned off. If the DVD player surround output is connected to the left input on the amp, oscillation occurs. However, if the power to the entire video equipment is disconnected, the DVD player can be connected to the amp without adverse effects. This suggests some sort of loop between AC power line and amp audio in/out.
Amplifier inputs are at same ground potential and both connected to amp chassis.
When left channel is connected and popping occurs, a large voltage difference between chassis and rack appears. This was discovered because arcing was observed between chassis and rack when amp was loosely sitting in rack. This was repeated several times to verify that it was not imagination.
When amp switched on and off (before speaker relay has a chance to close), 4-5 seconds later, a loud popping sound is heard in the right and possibly left speakers, and chassis voltage difference appears. (Note, speakers are theoretically NOT connected to amp as the relays are supposed to be open.)
Problem persists no matter which branch circuit amp is connected to.
Speakers are not connected to building ground; they are floating, as their only connection is the amp’s output terminals. The only persistent connection to the speakers is the chassis ground (the relay only disconnects the ‘hot’ side). If one side is disconnected and the ground side is moved to a different potential, how can substantial current flow in the voice coil?
Even stranger is that when a
battery-powered WAV player is connected to the amp inputs, the amp plays
fine. If the portable player is connected to the left input and the DVD or
the mixing board is connected to the right input, the portable player’s
signal can be heard in BOTH outputs.
The suspect amplifier was replaced with an identical Hafler 500, known to be
working, and it too exhibits the same motorboating problem when some
AC-powered signal source is connected to its LEFT channel input. Connecting
to the RIGHT channel input, it behaves normally.
The offending motorboating noise appears at the INPUT jack of the amplifier WHEN THE SPEAKER RELAY CONNECTS THE SPEAKERS. The output of the amplifier is a replica of the input signal, only larger.
If a tone signal larger than 100mV is applied to the amp input from the mixing board, the motoboating stops—however the sine signal becomes an overshooting (rising edge) square wave with a rounded trailing edge.
Thought: it seems as if somehow the AC power circuits are acting as a positive feedback loop for the audio circuit. There seems to be common mode conduction going on, but cannot figure out why the common mode path appeared without any user intervention, during a movie. No one touched the racks when the oscillation started for the first time.
Neither can I explain how two independent amplifier channels behave like they are connected together as mono when one input is connected to the mixing board or the DVD player, while the other is connected to the portable player. The Hafler 500 employs no means of switching to mono with one or two inputs connected. The spare Hafler 500 behaves the same way, so I’m inclined to believe the problem lies elsewhere.
When I run the amp in the shop, it
works normally. When I feed either of the suspect audio sources to the amp
WHILE IN THE SHOP it works normally. The common denominator seems to be that
the amp misbehaves only when in the rack. Even when electrically isolated
from the rack rails with rubber and cardboard strips.
I have been working on this problem all night and all day today, but am no
closer to a solution. I even checked the main breaker panel and tightened
all the ground screws. No other electrical problems in the house. The rest
of the sound system works normally. It is just the one amplifier used for
the surround that suddenly doesn't like external sources connected to its
LEFT channel input.
None of this makes sense, but I tell you that I could not make this up if I
thought about it all night! It's just too incredible. All the standard
troubleshooting methods were used, but the common aspect is anything
connected to AC power, WHEN THE AMP IS IN THE RACK. It's happy on the shop
bench with any source. But not when sitting in the rack, even isolated from
the rack, or even with extension cords bringing AC power from another branch
circuit. The proximity to the rack seems to be a factor.
In fifty years of working in electronics, I've not run into anything like
this in the field of broadcast engineering. But here it is in my own home
studio and all the classic remedies are ineffective.
Almost 24 hours TO THE MINUTE since this problem mysteriously appeared, it
vanished!
I had pulled the amp from the rack 20 minutes ago, leaving slack on the
wiring enough to set it on a crate in front of the rack. I powered it up and
it worked normally.
So the next thing I do is take an alligator lead and cautiously touch the
amp chassis with one end and the rack with the other, fully expecting
fireworks. Not a thing happened.
So the next thing I do is carefully lift the entire amp and sssllooooowwlly
slide it into the rack space where it normally sits. Again, NOTHING unusual
happens. So now I'm really wondering... The next thing I do is put one screw
in. Still no fireworks. I put the rest of the screws in. It's still working!
Next test: I power off the amp and power it back on. Still works.
Now let's try the other surround source (at this point I have it working
with the front end mixer output, something it would not do for the last 20
hours.) I swap the input connections with the output of the DVD player's
surround outputs. I power the amp up and... no popping. Just surround
program coming out of both channels as it should.
The bottom line is, this goes down in my "X-Files" folder. It's something I
cannot explain. For exactly 24 hours, no matter what I did, I could not
solve the "feedback loop" or whatever phenomenon was occurring. Now it's
working and all I did was install the amp while it was powered on. The other
7 or 8 times I installed it in the last 24 hours it was powered off. Go
figure. I'm not a mystical man, but this occurrence is deeply disturbing
because I have not found the cause of the problem, and it cleared up just as
quickly and mysteriously as it appeared last night.
MOTION PICTURE PROJECT/NEW VIDEO PRODUCTION FOCUS/ETC.
Good morning, fellow audiophiles. It's been a busy month and I haven't had much opportunity to write in here, but here's an update at long last.
To begin, I have been working on a motion picture project this month. I am doing a combination of CGI and live action shooting. The budget for the project necessitates that as much as possible be filmed without on-location shooting, as some of the scenes would involve hoisting cables between bucket trucks and flying a camera toward a house. I spoke to the writer about the plausibility of the script and offered to rewrite the opening scene and in doing so, volunteered my skills as a 3D animator to the project. So what we decided to go with was a camera fly through, approaching a house, then flying in through the window. This was a challenging shot, and I wasn't sure if I could pull it off in a convincing manner. Nevertheless, i worked at it, and within two evenings had generated some promising animation and match-motion video. The shot took into consideration the angle of approach, and knowing that angle, I was able to install an aircraft cable in the studio, to fly a video camera along the same vector as the "virtual" camera in Maya animation software. Some careful timing, derived from testing several video shots revealed a suitable motion for the camera and we had the actual actress come and do the scene a week later. The footage works well with the CG animation segment. The camera appears to fly through someone's back yard about 80' and in through an open window, transitioning to the live action footage. All everyone could say was "wow!"
During an ADR session for this film, I met someone who expressed an interest in becoming my business manager. Over a span of two weeks, we strategized and worked out an arrangement. We're forming a new company, a limited-liability corporation which is 100% focused on video production. No more confusing engineer/video production. This one is all video production and all the supporting services, including sound recording, DVD mastering, packaging, editing, and so on. My new business manager will be drawing upon her considerable sales skills to bring us specialized work. 2008 looks to be shaping up as an exciting year. BTW, we're about to launch the new web site, www.MWHDVideo.com.
XDCam EX... what can I say? This is the "must-have" video camera for our HD productions. There are so many drastic advantages that this camera has over the competing formats on the market and, almost regardless of price, it produces about the best picture anywhere. I've seen quite a bit of footage and pulled still images that looked like they were shot with a D-SLR with an expensive prime lens, not a video camera. In fact, they make the 1080P V1U footage look like 720P by comparison. The 720P output from XDCam EX is as detailed as 1080P output from HDV cameras. It's just incredible! So I'm trying to move Heaven & Earth to get one by this spring, and a second one by mid-summer. That means more equipment will be going up for auction in the next few months.
The symphony recordings I did last October are in duplication now. All production/editing is completed. All approvals from the conductor, staff and soloist are "go" and we're just starting to duplicate the DVD and CD. Every orchestra member gets a copy. This is a nifty form of marketing.
That recording is getting me some nice exposure. In fact, my new business manager was so impressed by it, she wanted to become a part of the company. I have also had visits from an audiophile magazine writer, and several other people with similar interests in the past month. The consensus is that I have something pretty good going here, with my proprietary recording method.
Blu-ray disc. I'm starting to experiment with authoring this advanced HD format. Last month, I made a test BDMV format on DVD-5, as an early test to see what sorts of challenges face the production process. Amazingly, the disc was readable in my new Sony BDP-S301 Blu-ray player. However, the data density on a DVD-5 cannot keep up with the Blu-print video format, which averages 35mb/S. But the picture looked great, albeit stuttering. So the next thing I am looking for is the new BWU-200S dual layer Blu-ray burner, so I can begin testing on real high density media. The scary part will be creating more advanced discs with interactive menus. It seems that when I've finally mastered Scenarist, the industry moves to Blu-ray. Blu-ray makes use of Java script, so authoring will be a complex process (as if authoring conventional DVD was easy.)
In the process of building a new web site, I am trying to learn Flash. More specifically, ActionScript. No matter how much I try to avoid programming, it's unavoidable when it comes to producing a great interactive web site. Brain expansion is a good thing, especially at my advanced age--that and vitamin E. :-)
And last but not least, I migrated my old desktop general purpose web authoring/e-mail/audio workstation to a newer machine. It was the hand-me-down from the old video editing workstation. The new editing workstation made another Windows XP workstation available, so I decided to decomission my older Windows 2000 PC and move the former editing workstation to fill it's place. It;s a bit faster, has lots more memory and is a LOT quieter. I lapped the heatsink on the CPU and improved the thermal transfer enough that I was able to drop the CPU fan speed from 50000rpm to 3000rpm, which drastically cut the noise. It took a couple of weeks to get most of my frequent-use applications installed and properly configured, but it's working pretty well now. Quite a few things do work better with XP. Even the Kurzweils and my legacy scanner.
One more thing: that service outage last weekend that took all of my domains offline, making our server inaccessible... we had a domain registrar, DirectNIC for all of our domains, but after the three-day outage, I decided to move. Basspig.com is in the middle of the domain transfer process. It's supposed to happen in the next 7 days. I don't know why they are taking so long, but that's the way it is. So if we are unavailable for a few hours in the next week, that's because the old domain was moved and has to be configured on the new registrar to point to our server.
NEW DOMAIN REGISTRAR, FASTER RESPONSE TIME & RETRO MOVIES
Moving away from DirectNIC turned out to be a considerable plus, after the DOS attack of their servers took all of my sites offline last week. Despite numerous trouble tickets in to their tech support, citing long delay times before the domain would forward, the issues were never resolved. The last nail in the coffin was that DOS attack/outage. I pulled up stakes and moved to Namecheap.com. And as soon as the DNS transfer took place, the page load times improved drastically. You probably noticed when you loaded this site today, that you didn't have to wait 3-8 seconds before the home page started loading. Oh, and another side-benefit: I'm paying about $5/year less than I did with the old registrar. Gradually, I will phase all my domains over, as they come up for renewal.
I don't keep up with what's going on in today's movie world. Having said that, several times in the past couple of months, I had the desire to see The Omega Man starring Charleton Heston again. I had seen it at a drive-in movie theater in 1971, as the first half of a double-feature with Downhill Racer. Looking up the Blockbuster web site, I saw they had it on Blu-ray. So on my next trip to rent, I sought it out. Unfortunately, the stores don't carry all the titles that the web site lists, so I had to settle for a plain old DVD version instead. It was nice to watch the film again, after 37 years. I was amazed at how well I recalled many aspects of the film, including specific lines and even some of the sounds, like the sound of the generator that provided the last source of electric energy for the last man on earth. Somewhat to my chagrin though, the soundtrack was mono and the quality of it was reminiscent of that old die cast aluminum speaker that the drive-in theater provided for hanging on the glass of the driver's car window. It was megaphone-like and distorted whenever anyone shouted. Optical soundtracks on film have never impressed me with their fidelity or dynamic range. Despite that, it was still one of my favorite "sci-fi" movies of all time. Ron Grainer's music was sort of blasé, but it had its moments of memorable themes. Overall, an enjoyable film to watch, though seeing it from a 2008 perspective, the 1971-ness of it really stands out as cultural shocker. It was indeed a breakthrough movie, in the sense that it featured a romance scene between a black woman and a white man. 1971 was indeed the height of the "black power" movement, and so co-screenwriter Joyce Corrignton, who was teaching at a black university at the time, chose to write this element into the script. Watching it back in 1971, it seemed "normal", but hearing some of the lines again in 2008, the campy-ness of the colloquialisms of that era struck me silly. In fact, I burst out laughing when Rosalind Cash (Lisa) utters her first lines, ordering Neville around at gunpoint. A nice little bonus on the DVD was a featurette on the making of the movie, including an interview between Heston and world-famous anthropologist Ashley Montagu. "There are no phones ringing!!!" Oh, the memories.
And more memories... for years, I'd been looking for an obscure TV drama entitled The Cube. I remember seeing it the night one of my cats was giving birth to a litter of three. It was an oddity at the time, which was February 1969. The Cube was about a man who somehow ended up in an 8'x8' room and who seemed unable to leave. A parade of various stereotypical persona entered that room, basically telling him how good he had things in there. In the end, they seem to be celebrating his "graduation" from the Cube, but the room and the people fade away and he is back in his cube again. Only recently, I discovered this was the brainchild of Jim Henson. Long forgotten, in the wake of the success of The Muppets, The Cube is relegated to the obscure cult TV show, having only aired twice (in 1969 and again in 1971). Once again, the trappings of the 1960s are blaringly-apparent, from the hair style of actor Richard Schaal, to the many people who visit him in his cube, through their colloquial behavior. I was finally able to watch it again, once again, serving as a kind of "checksum" on my recollection of the events of that obscure show. Watch The Cube on Google.:
THE INCREDIBLY-QUIET MOTU 896
This graph says it all:
The lower trace is the MotU 896 mic preamp with the gain set to the level at which I normally record orchestras, but with no input source connected.
The upper trace is the same recording device with a laboratory signal generator (Wein bridge oscillator) feeding it a 1KHz tone. (It's an older generator and is quite high in harmonic distortion.)
The reason I did two tests was because I didn't believe the noise floor figures. I just had to find out if the trace would approach 0dB with a full input signal--it did. All I can say is WOW!
I knew the preamps/A/D converters on this unit are extraordinarily quiet, as I never could hear any audible hiss in my recordings, but I had not realized they were THIS quiet. I tested with and without signal to verify that the measurement was really conveying the full range of signal levels. Anything better than -100dB and you're doing pretty good, I figured, but these numbers are just off the charts. Of course my signal generator is not nearly as quiet, showing a noise floor in the -90s.
This was a pretty exciting discovery, so I had to share!