Jump to content

borjam

Members
  • Posts

    269
  • Joined

  • Last visited

  • Days Won

    3

Everything posted by borjam

  1. Indeed, and low frequencies tend to mask higher ones. I am sure of that. Moreover, "traditional" techniques to enhance bandwidth over very noisy channels deal with "natural" causes of signal degradation. Examples would be communications with space probes orbiting near the Sun or, for example, the work of Joe Taylor on low signal data transmission modes with bandwidths in the range of bits per second. Not even hundreds! Digital lossy compression on the other hand can butcher signal integrity in very curious ways. The modem example I mentioned is interesting because probably the designers of the compression system decided to allow 9600 bps modems to work. In the PPM vs MP3/AAC case, however, it's just completely opposite goals. Explaining it in a somewhat extreme way, lossy audio compression systems interpret the bit strem according to a psychoacoustic model and resynthesize them. I wonder wether someone has came up with a scheme robust enough to survive that. It sounds challenging and (intuitivelly) I am not really sure it would even be possible at all. Maybe playing with timing tweaks, but we are good at detecting that. Now, let's be careful. Imagine some crazy politician reading us and thinking about mandating a universal re-encoding of audio and video content over the Internet in order to avoid steganography
  2. That’s a difficult question, it would depend a lot on the details. There are data encoding methods that can withstand lots of abuse, but mostly “analog” abuse (ie, noise, multi path interference, etc). Of course at the cost of bandwidth, Information Theory is after all one of the hard limits in nature, like Thermodynamics. That said, if I was the designer of that thing I wouldn’t try to make it error tolerant. After all the rest of the protocol stack will take care of that and email or web page content are transmitted over lossless paths. I would include some error detection mechanism but that’s it. They are using the audio file just because it will be considered harmless. And using steganography they can avoid some detection mechanisms that can identify properties of computer code. But that’s it. I remember (old story) when some phone companies in Spain begun using audio compression in their trunk circuits. Suddenly 28800 bps modems were unable to link at a data rate above 9600. Of course those modems had the ability to negotiate a data encoding scheme. One of these steganography files would not make it. Moreover, error tolerance depends basically on redundancy. Redundancy undermines the security of encryption, they are two opposite goals. Any property invariant through several transformations will at the same time make cryptoanalysis much much easier.
  3. @simmiz Now that I remember, this guy in Greece sells PCBs with a proper coplanar transmission line that would help with signal integrity. You could mount a Minicircuits balun on them, they have several parts that would work. https://www.sv1afn.com/rf-experimenter-s-pcb-panel.html
  4. @Jay Rose It seems to be steganography. In this case it's not a WAV file exploiting vunlerabilities to run malicious code, but a mechanism to distribute new code to already compromised hosts. Why a WAV file? Because firewalls and other malware detection systems won't intercept them. So, no need to get paranoid about WAV files. The risk would be the same if it was kitten pictures. Anyway the potential risks in all this are mostly a Windows thing. I remember the latest twist I have seen recently. I am receiving email messages with attached malicious files in .tar.gz format (a Unix file format). Turns out that modern Windows systems can open them. But if I upload the malicious .tar.gz file to Google's Virustotal.com (where a farm of anti virus systems check it), most of the antivirus programs complain of an unsupported file format! Windows has always had a critical problem with consistency when dealing with the meaning of "opening" a file, which is not such a simple thing because a file can be data or executable code. And they have traditionally made a huge mess with it. Apple haven't been free of foolish decisions but they have done vastly better.
  5. Hmm I wonder wether the PCB layout might cause more losses than the balun itself would solve. The real expert on this is @LarryF. The only baluns I have built for UHF frequencies were narrow bandwidth ones based on transmission lines (ie, a piece of coax). I used them successfully for TV reception with a homebrew dipole array.
  6. Looking at the photo, it seems you can disconnect the preamplifier or even insert an attenuator depending on the gain you choose. Of course provided the block diagram really describes it. However, I guess the gain selection switch might need DC power in order to operate. I don´t see a photo of the switch itself. But in that case you can use a simple bias-tee like this one. https://www.amazon.com/Bias-Tee-10MHz-6GHz-Broadband-Frequency/dp/B07RZSPQD9/ref=sr_1_1?keywords=bias+tee&qid=1570475344&sr=8-1 Of course, this is just an educated guess. Beware active antennas without filtering in front of the preamplifier though. HTB1xeBlaojrK1RkHFNRq6ySvpXaF.jpg.jp2
  7. I am pretty sure it's not the case. The problem is, really, you can't blame them. Anything touching consumers nowadays (and SD memory cards are!) is a bloody jungle.
  8. I am not using them myself but I have a MixPre 3 and its maximum sample rate is 96 KHz. That said, some comments about SD cards. - Counterfeits. Sandisk is much more likely to be counterfeited. I have several Sandisk ones and so far I've been lucky. But with Sandisk you have a risk of getting a counterfeit. In theory Amazon is a safe seller as long as you are buying from them instead of a third party vendor. But I've read confusing reports about inventory commingling. - Specification stability. The cards sold by Sound Devices are probably manufactured by Sandisk but (this is an educated guess) I imagine they have a contract against unexpected component or specification changes. So with a SD branded card you are less likely to suffer a nasty surprise. - MixPre II. Again an educated guess, but they are using a more powerful SOC (system on chip) which means that it will have resources to be more resilient against memory card hiccups. All that said, Compact Flash is orders of magnitude more robust but it's much more expensive.
  9. I haven't ordered in ages, but at least several years ago Sony was really good at providing parts. I would begin by asking the nearest Sony official service. At least in the past they had some service centres that also were the part distribution points. Of course they didn't stock most parts but their logistics system guaranteed that they would supply it even if it had to be brought from Japan. It was only a matter of time, from a couple of days to a week or several weeks.
  10. That is pretty clear It will make your life easier, but good audio will still require a pair of ears and some quality gray stuffing between them. Remember the common language version of the 1st Law of Thermodynamics: "There's no free lunch".
  11. Well, for example that headroom gives you freedom from clipping the stereo mix if you raise the levels of the mix faders too much. Yes, it’s a huge headroom. But sample formats don’t usually come in tailored sizes, like “I need 27 bits”. And if they are using the arrangement to increase the resolution of low level signals, well, that’s an improvement.
  12. That's a good question. Maybe the SOC they used for the original series was too limited and the ones in the series II have more power. The preroll time has been increased to 10 seconds, it's a good hint.
  13. I'm one of the skeptics except for this phrase in a Taperssection post by Paul Isaacs: Having said that, for the majority of sound recording applications and for those who know how to gain stage, 24-bit has always been way more than enough to capture high fidelity recordings when combined with high quality, low noise/low distortion microphones, preamps and ADCs. That hasn't changed. So then, why the big deal with 32-bit float files ... Of course, nothing wrong with making life easier for the user! I can imagine lots of situations in which this can save a lot of time, I guess for example FX recordings. But remember, your dynamic range is limited by the microphone and the noise floors of every step in the signal capture/processing chain. I can imagine the greatest benefit of the 32 bit files will be that you can't overload the L+R mix, something that can indeed happen with 24 bit files despite having clean, properly recorder ISOs. Of course not a sad day for me, happy owner of a MixPre 3. It's great to see that the line is being successful and SD are committed to develop it further.
  14. Oh sorry, silly me. He doesn't have any wireless audio specific stuff but maybe he can design custom equipment. https://www.jghitechnology.com/gb/
  15. Speaking of filters, I stumbled upon a small company in Italy (I think it's a one man show) that makes some really nice ones. I just purchased a FM broadcast notch filter for a project at the university and the specs are unbelievable. Although he lists several filters on the web page, I think he can make custom ones. Not the kind of filter needed here (our challenging use case, a wide band listening post which comes closer to ingelligence gathering operations than motion picture filming) but the attenuation figures at 108 and 118 MHz are pretty spectacular. ZNL_ScreenShot_2019-05-29_10-41-37.PDF He was slow to ship (took longer than a week) but I think this filter (which is not listed on the web page) was custom built on demand. So no complaints in that department. And the prices are very good.
  16. Although I am sure top manufacturers include extensive filtering, filtering is still mandatory if you use some kind of amplification. For example if you use splitters, which imply some attenuation, you may need an amplifier between the antenna and the splitter. And that amplifier should always have a properly filtered input. Otherwise all kinds of evil can happen.
  17. I think he was Gordon Willis? I recall I read an interview somewhere where he admitted that he overdid it in The Godfather
  18. Specs wise the Rode NTG3 might be at least close. I imagine the sound will be different but unless you are recording dialog it probably won't be much of an issue. I own a NTG8 myself and it works very well outdoors. I also did a brute force test of RF immunity and I must say both the NTG8 and the MixPre 3 passed with flying colors.
  19. Sorry to chime in late, It's being a really hectic week (my father passed away on Sunday) so I didn't follow the news much. The vulnerability is a serious design flaw because it launches a web server in the user's computer. That server is only accessible form the local computer. You can't connect to it from the Internet, but it's possible from a program running in your computer. So it is still available, for example, to your web browser. Remember that web browers are not just document viewers. Many years ago a programming language was added (JavaScript) so it can be a dangerous combination. Although Zoom's response to the first disclosure was far from stellar (at first it seems they were unable to understand why launching that web server is an Extremely Bad Idea™) they have now released an update that solves the issue. Getting rid of the software is also easier thanks to a comprehensive uninstaller. Some colleagues who were using it have confirmed that indeed the web server is done. And hopefully Zoom have learned a hard lesson.
  20. Have you seen that Rycote sells larger Lyres for thicker microphones? https://mymic.rycote.com/products/lyre/modular-lyre-upgrades/pair-of-duo-lyre-72-19_34-with-adaptor-screws/ The ones I used are designed for 19 - 25 mm diameter mics.
  21. I'm not sure about the original Blimp, but maybe this hack is compatible. Maybe they reused the basket and rail.
  22. The Rode Blimp 2 is a vast improvement over the first version. They upgraded it to adopt the Lyre suspension by Rycote, which is orders of magnutude better than the old traditional rubber ring suspension. Alas, it seems to be a half baked product and so far they haven't shown much interest on it. Two important flaws are: 1- The built in Lyres are too soft. Rycote manufacturers Lyres with several grades of stiffness. The possibility of using different lyres would be great. Sadly Rode decided to manufacture a sort of standard Lyre but with a built in adapter for the Rode rail, in a single piece. This makes it difficult to adapt Rycote spare Lyres. 2- Despite selling a long shotgun microphone, and a pretty good one at least for nature recordings, the NTG-8, they sell an extension kit which they say is only compatible with the first version of the Blimp. Turns out it's perfectly compatible with the second version, but the suspension Lyres are not stiff enough to support a long shotgun. See flaw #1. Fortunately it's not that hard to solve the problem. I purchased some spare Lyres from Audiosense (Belgium). I had no idea which variants to order, and they have modular and pre modular options. Pre modulars seem to be intended to upgrade older systems. The good news is, the pre modular is a modular Lyre with an additional adapter piece you can remove. To the left, a Rycote spare (in this case a Duo Lyre 72) and, to the right the built in Lyres from Rode. The Rode Lyre looks like a Rycote one but with the adaptor it would be molded in the same piece. It's possible to make such an adaptor (and I am measuring it and drawing it so that it can be 3D printed) but I wanted a quick test. After some minutes with a Dremel (don't forget your safety googles!) and a couple of plastic pipe attachments for 15/16 mm pipe I could finally make a couple of kludgy but functional Lyre adapters. (The not exactly precision cut grey plastic piece). Almost any rectangular piece of plastic with a hole in the middle will do, but there is one tricky problem: It needs to be within a certain heigth range, or the screw that links the Lyre and the bottom rail won't hold properly. The screw, the plastic adaptor and a bottom piece form a locking mechanism thanks to the pressure on the rail. About 10 mm is just right. I will complete a drawing of a possible adapter and, if possible, make a 3D model for printing. So how is it with the new Lyres? I would say it's much better. The Blimp is still very front heavy thanks to the long microphone and extension and using it on a boom pole for movie dialog would be considered serious mobbing on the boom operator. But it works fine for nature recording. I dare to say Rode chose the wrong "shore" for the Lyres. The 82 shore will support shotgun microphones much better.
  23. With a Mac it won't be much of a problem if you act wisely. Apple uses a really effective packaging system for program libraries, which means that there is not a chaotic system directory like "WINDOWS/SYSTEM" where everything is mixed up and the results can depend on the order in which you installed several applications. There have been idiots developing software for Mac OS X, like Logitech installing a silly "application enhancer" library in the System folders and rendeding the system unbootable when updating to Mac OS X 10.6 (Snow Leopard) but I think Apple slapped them properly and it's more unlikely to see an incident like that again. As for system updates which can be important for security yet detrimental for fragile software like ProTools, I always recommend to use a different web browser (which is the riskiest application in the system) that you can update without fear of affecting ProTools; its code is separated from that of the operating system. Between Firefox and Chrome I would say Firefox. Google has the bad habit of installing invisible auto updaters and, besides, Chrome has a couple of system extensions functionality that I consider potential suicidal stuff (Native Code, etc). So, install Firefox.
  24. Just try not to stick them together. It's better to keep some distance between them, roughly speaking more than half a wavelength or a wavelength. A metal element too close to an antenna can detune it and degrade its performance. It would be most noticeable if you are using specialized antennas (like the "hatchet" shaped log periodics). Also, it's better to arrange them vertically. If they are arranged in diversity pairs you can try to add two "masts" to the cart, with each member of a diversity pair attached to a different mast. And for the masts you can use some non conductive stuff. Fiberglass, PVC... I have found a thread about cart attached antenna masts in this same forum (surprising!): Other than that, unless the preamplifiers in the "boosted" antennas radiate any spurious signals (I guess they will be properly designed!) it should work.
  25. Not to talk about the huge privacy problems. However be careful what you wish for
×
×
  • Create New...