I suppose you have caught me out slightly lacking in precision or pedantry. A digital to analogue modulation scheme is able to exactly reconstruct the original digital signal within the design tolerances for noise and distortion. Yes, eventually a signal may degrade or be corrupted, but prior to that point the reproduction is literally and exactly perfect. That exactitude is just about the definition of a digital system. This bird system is incapable of reproducing the input image of the bird exactly. It is not a digital communication system, unless you consider the “PNG” of the bird to have not been the message being carried.

Yes, the near-identical sentences (only drawing a distinction between the processes where one exists) would indicate that. The “heard by the bird” and “reproduced by the bird” steps were also the same. But this is necessary context to make clear the digital data (“bit-stream”) that is being modulated into the signal.

It is far from “exactly the same”. The similarity is only in that both go through the same analogue channel. The entire point is that the modulated signal can be reconstructed exactly, while the spectrogram cannot.

The article title says they converted a PNG and the bird was able to “recall the file”, and yet it produced an indisputably different file. That it looks vaguely the same to the cursory human observer does not make it the same file.

Precisely… And digital modulation’s entire purpose is for a digital signal to survive those distortions bit-for-bit perfect. Even if we call the digitally-generated spectrogram digital information, the bird simply did not reproduce it exactly. Whatever time, frequency, and amplitude resolution you apply to the signal, if it’s low enough that the bird reproduced the signal exactly within that discretized scheme, then it simply did not achieve 2 MB/s. I would bet that the Shannon capacity of this bird is simply nowhere near 2 MB/s.

Exactly. Digital logic, when implemented in analogue, generally have to have forbidden zones where a signal in that range is considerer invalid. Regardless of implementation, digital is about the discretized logic of the system. That is explicitly the whole point of digital: Minor analogue distortion does not change the information content of the signal unless it is so bad as to flip a bit.

The whole sequence is:

• Digitally synthesized spectrogram (lossless)
• Played through a DAC and speaker to produce an analogue signal (lossy)
• Heard by the bird (analogue, lossy)
• Reproduced by the bird (analogue, lossy)
• Captured by an ADC as a digital audio signal (lossy)
• Spectrum-analysed to observe a similar (but corrupted) reproduction of the shape in the original spectrogram

To be transferring digital information, we would instead need to modulate and demodulate the digital signal (exactly like an old modem) so that the analogue corruption does not affect the digital signal:

• Image file (lossless)
• Bit stream (lossless)
• Analogue modulation of bit stream played through DAC (lossy)
• Heard by the bird (lossy)
• Reproduced by the bird (lossy)
• Demodulated to recover exact bit stream despite distortion (lossless again)
• Decode bit stream to recover original image file, bit-for-bit perfect

I extremely doubt that this bird is capable of 2MB/s. For reference that would make it 280+ times fast than dialup, and barely slower than ADSL. This setup is basically just using the bird instead of a telephone line.

Not to be a wet blanket, but every time this comes up I get annoyed by some factual inaccuracies in the articles about this. It is not digital! He drew an image on a computer, but converted it to an analogue spectrogram to store on the bird. That’s neat as hell, but it’s not digital. The image that he got back was slightly corrupted.

Now I would be fascinated to see a follow-up seeing if you can actually modulate a digital signal and have is survive a round trip through the bird bit-for-bit accurate. I suspect in reality it would be much lower data rate, but definitely not nothing!