Rewinding Live Radio

Even though it’s now a forgotten afterthought in the history of broadcasting technology, we often forget how innovative the TiVo was. All this set-top box did was connect a hard drive to a cable box, but the power was incredible: you could pause live TV. You could record shows. You could rewind TV. It was an incredible capability, that no one had ever seen before. Of course, between Amazon and Netflix and YouTube, no one watches TV anymore, and all those platforms have a pause button, but the TiVO was awesome.

There is one bit of broadcasting that still exists. Radio. For his Hackaday Prize entry, [MagicWolfi] is bringing the set-top box to radio. He’s invented the Radio Rewind Button, and it does exactly what you would expect: it rewinds live radio a few minutes.

To have a pause or rewind button on a TV or radio, the only real requirement is a bunch of memory. The TiVO did this with a hard drive, and [MagicWolfi] is doing this with 256 MB of SDRAM. That means he needs to access a ton of RAM, and for that he’s turning to the Digilent ARTY S7 board. Yes, it’s an FPGA, but actually a fairly simple solution to the problem.

The rest of the circuit is an FM receiver chip and an I2S audio codec on an Arduino-shaped daughterboard. The main controller for this project is a big red button that will simply rewind the audio stream a few minutes. There’s no telling exactly how long [MagicWolfi] will be able to rewind the audio stream, but 256 MB is a ton in the audio world.

35 thoughts on “Rewinding Live Radio

  1. There was a gadget I heard about on NPR called “what was that?” or something similar. A little self contained stick-on-the-dash button-on-a-box that would repeat the last 5 minutes like a flight recorder of what ever was coming out of the car radio. This would be handy for those senior moments and what were we talking about before…

    Oh, this could be an app in any phone. That would be handy.

  2. My 2015 Chevy truck has the rewind feature/DAR built into its sound system. I haven’t kept track but seems that I had it paused for at least a 1/2 hour on occasion. I love that feature!

    1. My 2017 Subaru has this too. I like it. It’s nice when I miss something, and automatically kicks in when the phone is in use. The on-screen controls aren’t that great… a big red button might be nicer. Even better: a shuttle wheel for searching back and forth.

  3. Interesting. Sorta kinda did this when the sticker shock for a hearing aid (4k USD) made me roll my own. Original design used a Teensy 3.2 and the PJRC audio board and the most wondrous PJRC audio library. Later copied stuff from the Open Audio project (see

    My hearing aid can play-back a conversation. Changed to Teensy 3.5, added FM receiver IC and wire antenna, but was getting to be a bit messy, so am putting the system on diet and using the more expensive Si labs FM chip and will think about a small flash addition for radio pause/playback (current SD card too slow). Immediate playback can the relatively monstrous heap space of the Teensy 3.5, but is limited because am using a single static allocation for sound playback.

    Mounts in a shirt-pocket container and sports a LED to let co-workers know if in conversation recording mode.

    1. In a PC I mean in case that wasn’t obvious.

      Also on the radio side, a number had FM turners with similar facilities in software. On Amazon right now I now there are radios with MP3 players built in that are like Radio “PVRs” but not sure they give the instant replay.

    2. Even then it was a pretty big gap in between the two, as I had both devices, 1st gen tivo plus an ATI catalyst all-in-one.

      The tivo made it beyond simple to record both things you knew you wanted plus things you didn’t know you wanted until during/after seeing it. The capture card could only deal with the first of those, and then only by setting a single channel in advance. The capture card was more useful for long term archival, as the tivo wasn’t intended for that and would get worse at its main task unless and until you upgraded its HD.

      A combined capture/tuner card would work pretty well and “tivo like” but was limited to over the air.
      For cable/satellite however, this was already past the time many providers required their craptop box to be used, and the tivo integrated easily where PC software did so poorly if at all. The tivo used the cable box and changed channels as and when needed. The ATI software I remember could barely integrate with IR-blaster and often got out of sync with the box itself. You had to turn on the box, set the channel, and schedule the recording, which had to take place before the box shut itself off 24 hours later. No sending a power on IR when it didn’t detect a signal for example.

      Personally I don’t think the myth-tv interface is to this day as nice to use, but opinion aside, back then even that didn’t exist as an option

      1. Yeah a lot depended on the software, and CPU and hard drive speed then, or whether you had hardware Mpeg anything encoders for what you could achieve in functionality. ATI card might have been OTA TV only but Compro and others had cable and satellite turners. I am thinking of immediately pre-digital era, there was definitely a time there were it “got complicated”.

  4. Sorry Mr. Benchoff, I’m compelled to bust you on this one… “There is one bit of broadcasting that still exists. Radio.”. Erroneous statements like that is how wrong ideas get on the road to be treated as fact.The switch to digital transmissions,doesn’t mean that TV broadcasting ceased. While I appreciate the effort and skill that went into producing this, I can’t see myself wanting one unless it’s made easily transportable. The only time I really listen to the radio is when I’m one the road.

    1. “Of course, between Amazon and Netflix and YouTube, no one watches TV anymore,”
      How millennial of you to say that.
      Many people still watch ATSC broadcasts free (commercial supported) over the air.
      Still, liked the article.

      1. I have the 4 channel version with 2TB of storage and I love it. I pay 9.99 a month for the service, ask nice and they will give you the reduced rate if you’ve been a customer for awhile. I want to love Hulu, but until I get the TiVo like experience ( I want the jump back a few seconds feature) I’ll keep my TiVo.

    2. He didn’t mean that they aren’t still broadcasting TV, he meant that nobody except old codgers are tuning into it anymore. But the average person is still relatively likely to be listening (at least once and awhile) to live broadcast radio.

      1. Agreed. Radio was pronounced dead a lot of times before and is still alive. Other more modern technologies are already gone for good. There are many people out there who just use what they know and don’t care about the modern stuff as much as we do.But then a radio rewind button might be too modern as well. I am just having fun doing this project for now.

  5. Why not use a cheap RTL-SDR dongle with SDRsharp and the “TimeShift” plugin from Then you can basically buffer as much as you have RAM in your PC, for real time use. But if you need longer than a few minutes of buffering, then you could always record with RAM buffering to disk using the either the “Baseband Recorder”, “IF Recorder” or even the “Audio Recorder”, and then use the “File Player” plugin to read back the saved files from disk. You could even use a HackRF to access 20MHz of RF spectrum.

      1. The only advantage of a hardware solution that I can see is that it could possibly be easier to tailor a solution for use by people who are visually impaired when compared to a heavily highly graphical interface with no keyboard shortcuts.

    1. There are umpteen ways to pause/delay/replay audio from radio, but a solution that requires hours of cludging together software from various vendors into hardware from an equal number of vendors just doesn’t cut it for me.
      A simple solution that just does what it is supposed to, and can be installed in places where it is required (which would you rather install in a car… this thing, or an SDR with PC plus power supplies, and the inevitable software glitches caused by poor power supply reliability). This thing is small enough to be installed into most radios themselves too.

      1. It can do audio as well (“Audio Recorder”), but I was also talking about a large chunk of RF spectrum which would include all digital as well as analogue modulation as well in an un-demodulated format (In-phase and Quadrature). I’ve installed four application in as many minutes, there is no great difficulty to it at all.

        1. THAT is more like it! An audio recorder in 2018 might be useful for a dedicated radio listener, but snarfing down big chunks of spectrum, so you can tune into stuff long after it was broadcast, is proper tricknology!

  6. Thanks Brian, love your article (obviously). And a special thanks for not including the last paragraph that always points to other ‘related’ articles. But maybe you just did not find anything related, which would be a big YAY \o/ from my side.

  7. The problem with all of these devices is they don’t record everything. When I say everything I am talking about the full radio or TV spectrum. Short of that, if you are a station flipper as opposed to loyal to a network, you delay a show so you can go get dinner, you rewind a couple of times when the dog barks and you could not hear it. Man that worked great you think. Until your show ends and you flip to another channel and the show on that channel is now in half over with no option to rewind. Oops. Now if you could record the full baseband, that would be cool. Probably not practical, but cool.

    Broadcast is dying anyway. On demand is where it’s at.

    1. Broadcast is still the cheapest way to serve millions of people who want to watch more or less the same stuff. 20 years ago or so I remember people were looking at tweaking the IP broadcast stuff, which back then wasn’t as developed as it should have been, to give video on demand without having to wastefully send a complete source -> destination IP stream per customer. The Internet itself is capable, apparently, of duplicating packets and splitting streams at the most efficient point, to let any number of users recieve a single transmitted IP stream.

      Then people stopped writing about it. Then 10 years later Netflix turned up. Is that how they do it? Or do have to send out a unique stream to each customer? I suppose that can be virtualised, like the content delivery networks that secretly backup and cache most of the www.

  8. I had something like this in the early 2000s and XP media center. It made for a decent PVR. The problem was there was no guide for the radio. But I could record for as long as I had enough HD for it. Heck it probably still works. Think it was something from Hauppauge. It had 2 tuners for cable and 1 for AM/FM.

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