Sunday, April 23, 2006

Mom and pop podcasts

One of the things I've wanted to do is interview folks over the phone. To do that, the first step was to find ways to make cheap telephone calls to any point in the world. The solution to that problem was to use a voice over IP service (VOIP), which I did. Many customers choose to connect a VOIP phone that plugs into their broadband router to act and behave like a regular phone. However, to be able to use the keyboard while conversing, I opted to use a free downloadable "softphone" -- a computer telephone -- which normally has an interface resembling a keypad displayed on the monitor. You then speak into and listen over a regular computer headset with a microphone, the kind you can buy in Radio Shack for about twenty bucks. There are few gotchas in setting a VOIP softphone, but not something that a two-fisted, hard drinking person can't solve. So the first part, making cheap calls to any point in the world, has a ready solution.

The second step was to find a method of recording VOIP telephone conversations (with the permission of the interviewee of course) and storing them as audio files. That turned out to be a little harder than capturing regular telephone conversations. To record a regular telephone conversation as an audio file, all you need to do is go down to the neighborhood electronics store and buy a fairly cheap pickup that will answer to the purpose. It takes the audio from both ends of a conversation and with a little more hardware record it in an audio format that can be saved to your trusty hard disk. Unfortunately, VOIP telephone conversations are not "telephone" conversations. They are actually packets transmitted in a particular protocol over the network. Therefore while Windows Sound Recorder, for example, will capture your microphone and headset sounds perfectly from the soundcard, attempts to record a VOIP conversation using the same method are doomed to failure. No amount of fiddling with input and output devices in the Settings menu will avail.

At this point one could go and get hardware that will essentially "tap" into the computer headset and record an audio file at the interface or shell out major bucks for a fully-featured VOIP recorder. These are typically manufactured for call centers so that they can record customer conversations for "quality control purposes". Heh. But unless one has a large and a half to shell out, getting a VOIP recorder probably isn't the best way to go. If your VOIP software happens to be a product for which a software recorder is available, then you can buy that for considerably less than a hardware recorder box. (Some software recording utilities are made for VOIP apps like Skype or Express Talk.) But if you, like me, use unsupported softphones then you must turn to capturing the VOIP network packets themselves.

This turns out to be easier than it sounds. The best approach is to download an open source packet sniffer, which is an application that will capture everything going through your network, including your VOIP traffic. Just turn on the sniffer when you make your call. Then having captured all the network traffic during the call, you filter the packets down to those of type rtp.p_type = = 8, which happens to correspond to the format of an a-law, u-law codec. (You might have to fiddle with the softphone to make sure it sends the packets in this format)  After applying the filters you will be looking at the VOIP call only. All the other network stuff has been filtered out. Then some packet sniffers (such as the one I downloaded) have the ability to assemble both the outgoing and incoming VOIP packets into one time stream which you can then save as .au or .wav file. And there it is. Your audio file is on your hard disk.

The last, optional step is to edit the computer audio file into something resembling an interview. That can be done by downloading free software like Audacity so that you can edit the interview itself. At this point you can dream of giving Rush Limbaugh or Howard Stern a run for their money. There, in a nutshell, is a guide to creating a podcast, which you can then get broadcasted in some fashion. The entire process described above requires no hardware other than your broadband connection, a soundcard, some hard disk space and a computer headset. Then, apart from your subscription to a VOIP service, the remainder is absolutely free. No money is required for the softphone or to record your VOIP conversations. Well not quite free. For those whose calling doesn't take them into looking at network traffic for a living it will cause some bother: a few hairs pulled in frustration and more than a few cups of coffee. I hope the readers of the Belmont Club find this post useful, even if it is slightly off the usual topic.


Some readers will be horrified to discover that their VOIP conversations are actually visible as unencrypted packets over the network. But unless you take special precautions that's exactly what they are. Something to bear in mind if you're using VOIP over the company network with an intrusive IT manager.


Blogger Tony said...

Heh There are few gotchas in setting a VOIP softphone, but not something that a two-fisted, hard drinking person can't solve. snicker

Funny stacked puppets

4/23/2006 07:54:00 AM  
Blogger Red River said...

Can you believe that most call centers still use hard phones and analog phone switches?

Its best to explicity allow all traffic, and leave it to the leads and managers to ensure that people are getting their work done. We are one of the few large shops that does not monitor web usage either. Makes IT's job a lot easier and lets us focus on real security.

4/23/2006 09:06:00 AM  
Blogger BeefStu said...

Wretchard, two suggestions come to mind for VOIP call recording:
1. Try out a little piece of software called TotalRecorder. From their site, "Instead of relying on the sound card, Total Recorder captures the sound stream directly from Windows, before the audio goes to the sound card." It works very well, in my experience.
2. Set up an Asterisk system for your VOIP. It can be configured to automatically record calls.

4/23/2006 09:22:00 AM  
Blogger said...

There should be a pure software solution - such as TotalRecorder suggested by beefstu.

For Mac OS X, for years we used the bullet-proof Audio Hijack Pro which can auto-record any sound stream:,1759,1712649,00.asp

Or if you use Apple's free Garage Band for audio recording, mixing & processing, a USB headset, and VOIP and you have a complete podcast studio for the cost of a USB headset.

Not sure how you do multiple phone interviews like Glenn& Helen are doing over VOIP. Perhaps they are using a conferencing phone and external audio input.

4/23/2006 09:48:00 AM  
Blogger RWE said...

An alternate approach ... while reeking of stone knives and bearskins ... is to use a cheap casette recorder and record the conversation in an manner completely independant of the computer - assuming that you are using the speakers as well as the microphone, which you probably are. Once on tape you can input it into a computer any number of ways for recording, editing, processing, making it sound like Alvin and the Chipmunks, etc. The little portable recorders even have a VOX feature, enabling you to not waste tape during pauses. The only problem is, be sure to CLEARLY say who you are talking to at the start.

Or go buy that big reel-to-reel you have always wanted for your "pirate" radio station ....
Just saw one for sale on the local airport bulletin board.
Of course a VCR is way cheaper, far easier to obtain, more practical to use and far more reliable - But not as cool...

4/23/2006 10:11:00 AM  
Blogger desert rat said...

cool rules, rwe,
cool rules.

4/23/2006 10:32:00 AM  
Blogger Buffy said...

This is great information. I always wanted to have a talk radio show to ruffle a lot of feathers. Bring it on.

4/23/2006 11:08:00 AM  
Blogger Common Cents said...

Instapundit is making fantastic podcasts. Best of luck with your endevour.

4/23/2006 11:51:00 AM  
Blogger wretchardthecat said...


I actually saw TotalRecorder while experimenting on this problem. But since it cost about twelve bucks I went on to try other methods and I got those to work.

I hope people don't get the idea I'm moving into podcasting. I'm not except maybe just to try it as an amateur. The motivation to attempt it was the simple desire to interview someone I could reach by phone if I needed to put that interview onthe web. As it happens you can do it for nothing, as described in the post. It's a fairly obscure approach to the problem, but I since I solved it (Took 2 cups of coffee) it seemed only right to share it with the readers.

4/23/2006 12:07:00 PM  
Blogger The_Head_Jimmy said...

I wonder how many people in North America are using voip to call, say, Pakistan for example...

4/23/2006 12:20:00 PM  
Blogger wretchardthecat said...


Radio Shack used to sell a gizmo with a sucker cup at one end and a line in jack at the other. This was the handset tap I was talking about to pipe audio into a sound recording device. If you jammed the line in jack into a device which recorded in audio file format I suppose that would work. Just guessing cause I haven't tried that approach though I considered it.

4/23/2006 12:22:00 PM  
Blogger Ash said...

They have a modern version of that 'sucker cap' you slap on the handset. You can buy a gizmo that you put between the handset and the phone which gives you a line out signal for recording. We set up a polling center with off the shelf MP3 players to record interviews which can then be uploaded to a hard drive for distribution. The problem with analog recording (i.e. reel to reel tape decks, vcr's ect) is that you have to recapture the sound and get it to mp3. By recording the interviews directly to mp3 you skip all those time consuming steps.

4/23/2006 12:30:00 PM  
Blogger wretchardthecat said...


That sounds like it would work. I should add that the packet sniffer approach described in the post will actually list out each and ever individual call you made over the time period of the packet capture, including the failed and rejected calls.

What you get is a list of VOIP calls and you can record each on separately. This is probably a standard feature among commercial products.

Thanks, BTW, for sharing your method.

4/23/2006 12:35:00 PM  
Blogger desert rat said...

GAZA (Reuters) - A militant leader appointed to a senior security position in the Hamas-led Palestinian government said on Friday he would not abandon the fight against Israel which has long sought to kill him.

Jamal Abu Samhadana, high on Israel's most wanted list as leader of the Popular Resistance Committees (PRC), was appointed on Thursday to supervise the Interior Ministry and set up a new police force from militants to crack down on anarchy and chaos.

"Factions and security services should unite in one trench against the daily Israeli aggression against our people," Abu Samhadana told Reuters in an interview.

Israeli officials said Abu Samhadana was still in the army's sights despite his senior appointment in the government led by the Islamist Hamas movement.

4/23/2006 01:23:00 PM  
Blogger RWE said...

Wretchard: I have not seen one of those inductive couplers for years and years. I used to have one. But I doubt it would work well with a computer - there is so much going on electronically there that it likely would pick up all sorts of noise.

Recently I videoed recorded a friend's performance at an airshow. I could not hold the AM radio used to receive the announcer commentary and the little video camera in one hand, since the camera jammed the radio quite effectively. A computer would be far worse.

Come to think of it, that same little camera will also do MP3s direct, using its own built-in mike.

The modern RF environment is simply stunning. And its getting worse. Someone should do an HG Wells War of the Worlds version where the Martians land and our household appliances jam their massive war machines into immobility.

4/23/2006 02:11:00 PM  
Blogger wretchardthecat said...


Well said. There's a concept called "electronic fratricide" which describes how a person armed with force multiplying electronics, jammers, etc can wind up stepping on his own d..k. I'm sure you are well aware of this phenomenon.

I've already got to three posts and I'm going to self-exile after one more to keep my own rules. Unless something breaks.

4/23/2006 02:21:00 PM  
Blogger Thief said...


One solution to the security problem is Tor (, which distributes packet data randomly among an anonymized, encrypted P2P network. I work at a law school, and I know a few people involved in sensitive human rights and FOIA cases; they swear by it.

4/23/2006 02:30:00 PM  
Blogger jd watson said...

FYI, I believe Instapundit uses an audio phone coupler and mixes on his (small) Mackey mixer.

My criticism of many podcasts is the very different audio levels of the interviewer and interviewee. I suggest running the tracks thru a compressor/limiter (plug-in) with the knee set at a low level (say, about -10 dbm) and the slope set at 2:1 to 3:1, and then increasing the level in the mix to compensate. This reduces the dynamics somewhat, but adjusts the levels so it sounds more like everyone is in the same room. Frequency equalizing is another topic: phone mikes probably cut some of the bass and the channel is bandwidth limited, so you miss the highs.

4/23/2006 02:39:00 PM  
Blogger wretchardthecat said...


Thanks for the tip. I don't need the network security but was afraid that if the bug bit me it would mean a couple late nights up finding out what the solution was, then another extended period figuring out how to implement it.


4/23/2006 03:07:00 PM  
Blogger Doug said...

Internet Video "Vs " Net Neutrality?

4/23/2006 03:26:00 PM  
Blogger James Smyth said...

you filter the packets down to those of type rtp.p_type = = 8, which happens to correspond to the format of an a-law, u-law codec

Packet Type 8 is A-law, not u-law. See IANA assignments of RTP Packet Type

U-law ("mu-law") is actually more common.

4/23/2006 06:43:00 PM  
Blogger Fat Man said...

"Something to bear in mind if you're using VOIP over the company network with an intrusive IT manager."

And they could not listen in on an analog conversation.

4/23/2006 07:37:00 PM  
Blogger wretchardthecat said...


Thanks for the heads up.

4/23/2006 08:07:00 PM  
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6/09/2006 08:37:00 AM  

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