Audio Calibration and Wiretapping 101
Today you'll know how to tap your network using Wireshark, how to fine tune your home theater audio, and more.
Wiretapping Your Home
Step 1: Get a Tapping device
- Gig, 10/100, aggregating, tap, hub, SPAN/Mirror port
- See episode 63 of “Know How”
- Padre prefers the Netoptics Gig Zero Delay Tap – But that runs $700-$1000 USED!
- A much more affordable option is the “Throwing Star LAN Tap Pro” from the HakShop - $39.99
Step 2: Get a device capable of receiving the tap data stream
- Anything with a WIRED port that is capable of receiving the full speed of your chosen tap
- USB adapters are fine, but remember that USB 2.0 devices top out at 480Mbps. If you’re using a Gig tap, you’ll drop traffic once the pipe is less than half full.
Step 3: Get Wireshark (www.wireshark.org)
- Mac/PC/Linux – 32/64bit – Choose the version that is right for you.
Step 5: Choose where to place your tap
- The tap will capture the traffic going between the two devices on either side of the tap.
- Tapping the Externals will give you ALL devices on your network.
- Tapping the Wireless AP will give you ONLY the devices connected wirelessly
- Tapping a specific desktop/laptop/set-top box will give you ONLY that traffic
- You choose if you want the outgoing or the incoming traffic.
Step 6: Capture
- Press the button!
- Choose the interface on your capture box. Typically it will be labeled "Local Area Connection"
- Click "Start"
Step 7: Analyze
- Looking for Outgoing Streams: Are you a Spambot?
- Filter for SMTP: Look for SMTP packets when your computer is supposedly idle
- Filter for DNS: look for sites you don't recognize.
- Looking for "Top Talkers
- "Statistics" – "Conversations" – "IPv4"
- Click "Bytes" to sort by Top Talkers
- You can see the origin and destination of your traffic
- Looking for Usernames/Passwords in the clear
- In the "Filter" field, type " – "tcp contains username"
- This will give you all the packets that contain the string "username" in the clear
- Looking for Network Congestion
- Here are a few helpful strings to get you started
- "ip.addr == 192.168.0.1: – This will give you all packets with 192.168.0.1 as either the source or destination.
- "ip.addr==192.168.0.1 && ip.addr==192.168.0.200" – This will give you all packets going between 192.168.0.1 and 192.168.0.200
- "tcp contains username" – This will display all TCP packets that contain the word "username" – I think the usefulness of this one is self-explanatory
- "tcp.analysis.retransmissions" – This will display all packet retransmissions – VERY useful when you've got a network that is unexpectedly slow.
Audio Calibration Part II with Scott Wilkinson
We've got part two of our audio calibration tutorial with Scott Wilkinson in this episode. In Part I of our audio calibration segment, we allowed the automatic calibration tool take care of our speakers. This time, Scott gives us the techniques we need to tweak our audio to create a great sound field.
To calibrate your audio, set your sound meter to 70 dB. Then you'll place your sound meter on a tripod in the center of the room. Play the test tone from your audio/video receiver (AVR). Scott calibrates each speaker to 75 dB. To get even better audio, you can tell your AVR how far your seat is from each speaker. You'll need to take out the measuring tape and find out the distances. From there, you can place those values in your AVR.
If you cannot find your AVR's onscreen menu, you might want to connect your AVR to your TV via the composite (or yellow RCA) cable. Scott says that older AVRs feed their onscreen menus through that connection, which may seem counterintuitive to many.
You'll also tell your AVR if your speakers are large or small. The physical size of the speaker isn't what large or small refer to -- those words relate to what frequencies the speaker can reproduce.
Speakers and Subwoofer Tips
Any information that cannot be produced by a small speaker get redirected to the subwoofer. Scott's general recommendation is to tell your system that all your speakers are small. Don't worry about sending your low frequencies to your subwoofer because those low frequencies are non-directional. You'll hear what the director intended.
Where should you place your subwoofer? If you want to find the optimal place for your subwoofer, try the subwoofer crawl method. Place the subwoofer where your seat would be. Then play a familiar piece of music that has plenty of bass. Then crawl around the outside of the room. Wherever the music sounds the most natural is the place you should put your subwoofer.
When it comes to your audio cables, make sure you've got them set right; red to red, black to black. Mixing them up could lead to phase inversion, which causes indistinct audio.
The last step is finding the frequency below which you send audio to the subwoofer. This is also known as crossover. THX suggests 80 hertz. Scott suggests that you look at the specs of your speakers. If your surround speaker goes down to 100 hertz, Scott would set the crossover to 100 for all the speakers to create a consistent sound field.
Scott recommends that your five or seven speakers all come from the same manufacturer and possibly the same line. Individual manufacturers tune their speakers differently and to have a consistent sound from those speakers, it is easier to have speakers from the same manufacturer. Your subwoofer doesn't need to be from the same company.
We got a chance to ask Scott four questions to get more information out the Home Theater Geek. We've given you a summary of the Q&A, but you'll have to watch the video or listen to the audio to find out the full answers.
1. Is there ever a reason to leave motion smoothing on?
Scott says yes, for things shot on video like sports or news.
2. Can you replace your speaker wire with coat hanger and not notice?
Scott said he wouldn't because the hanger isn't insulated nor is it flexible. Sonically, it might not be a problem.
3. Is there ever a good reason to place a TV over a fireplace?
No, the angle's all wrong.
4. Movie theater popcorn: lots of butter or light butter?
Neither. Scott doesn't eat popcorn.
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