Upgrading a voice recorder with a hex editor

[Alex] just bought a really nice TEAC VR-20 audio recorder, a very capable recorder perfect for recording your thoughts or just making concert bootlegs. This model was recently replaced by the Tascam DR-08 audio recorder. It’s essentially the same thing, but the Tascam unit can record at 96kHz, whereas the TEAC can only record at 48kHz. [Alex] figured out a way to upgrade his less capable but cheaper VR-20 to record at a higher bit rate with just a simple firmware hack.

The mod began by downloading the firmware for both the TEAC VR-20 and the Tascam DR-08. Both of these sets of firmware were exactly the same size, and after downloading a hex editor, [Alex] found a huge difference in the first 20 bytes of the firmware – the portion that tells the microcontrollers what it actually is.

The solution to improving the bitrate for the TEAC VR-20 was as simple as copying the first 20 bytes from the TEAC firmware over to the first 20 bytes of the Tascam firmware. After that, it’s a simple matter of upgrading his TEAC and getting the ability to record at 96kHz.

A very, very simple hack that’s really just flipping a few bits. Not bad for a two-fold improvement in the recording capability of a handheld audio recorder.

PIC-based voice recorder

[Vinod] just finished building a voice recorder and it turned out even better than he thought it would. The video after the break shows him recording what is surely one of your favorite songs from his cellphone and then playing it back. The audio quality does sound quite good for a project with very few components.

A PIC 16F877A makes up the majority of the build. Its ADC is used to capture the incoming line from an amplified microphone input (you’ll find that amp schematic half way through his post). He’s storing the data on an MMC card, which was a bit of a hack since the PIC has limited RAM to manage that overhead. The stored data is in a raw format, as the card is not accessed using a file system. This makes it easy to record at a high bit rate, leading to better audio quality. Playback consists of connecting a speaker via a low-pass filter and amplifier circuit to the hardware PWM output on the PIC.

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