Digital Audio Compression - Computerphile

How does rich audio compress to stream across the internet with little quality loss? Audio Analytic's Dr Chris Mitchell explains.

Audio Analytic is a sound recognition software company based in Cambridge UK & Palo Alto USA.

.mid files: Wikimedia Commons

This video was filmed and edited by Sean Riley.

[Lolwutdesu]

Sometimes computerphile does incredible videos. Then there are videos like this, which literally tell me nothing.

[kevnar]

One time, my cousin was bragging about how he converted his songs to a totally lossless compression. He went on at some length about how he could only fit one album on his entire music player because the files were so big. I just nodded and told him, "You might as well have not bothered if you're listening to the music on those crap headphones." I feel bad now for ruining his experience.

[RS-ddyv]

The emotion behind explaining something fascinating... mind-blowing!

[presswt]

Isn't it just wrong to say that MIDI has "lower quality" than other formats?
MIDI is playback data, not the same as an audio RECORDING.

[st_ProCactus]

The best thing about the MOD format is anyone can make samples and easily transfer their work.
The variety of samples to use was never ending.

[michaelkreitzer]

As somebody with a background in software dev and IT, this really didn't help at all. It was a very long version of "it doesn't encode the bits you can't hear." I suppose if I really cared I could just research it properly, but I was hoping for a little better laymans description.

OK, so, say I have a recording at X Hz and 16 bits per sample for 1 second then I have X*16 bits of data. The way he described it it sounded like uses something like a fourier transform to break into multiple tracks of variable Hz and variable bits. However, even if you broke it down into as little as 5 bands then combined they couldn't have more than a bitrate of (X * 16) / 5, and no single band could be close to the original resolution before the file balloons to a much bigger size.

There's a huge gap in how, exactly, separating the frequencies into multiple tracks of differing resolution can then be stored in a way that doesn't produce a larger file.

That make sense?

[dosmastrify]

Yeah i agree, this is a more popular level info dump than typical deep dive we expect from computerphile

[NorthshireGaming]

I remember quite vividly my earlier online adventures when downloading MIDI files were a completely relevant way of downloading, usually video game music for me at least. Since the MIDIS were little more than "sheet music" in digital form, it allowed you to modify which instruments were played for each track. A MIDI played on one computer could sound completely different on another depending on the sound card was present on the machine.

Early MP3s sounded tinny and would be scoffed at in regards to the audio quality by the standards expected today. It wasn't unusual to see MP3s shared at 96-128kbps, which is dreadful, but was necessary to accommodate the limited space available on early MP3 players limited storage - which could be anywhere from 32-64MB.

We'd eventually see CD players that would support the MP3 format, which would allow you to store hundreds of megabytes of MP3s on a compact disc.

At a time when internet transfer rates averaged 3-5KB/sec and and data storage options were limited in the MB range, MP3s really were a godsend.

[ckmishn]

Someday you should do a video about the software patent clusterfuck. Audio compression is just one area where software patents created a huge mess.

Granted it's an area of law rather than computer science, but it has had a major (mostly negative) affect on software development.

[unvergebeneid]

Interesting topic, needs more love than it got from this short video!

[PrashantBatule]

What I understood from the video :-
1. Humans can't hear every frequency significantly due to vibrating restrictions in the membrane inside of our ears.
2. So we delete this information from the audio file to reduce it's size.
3. We have become better at doing step 2 (?)

[sharks]

You forgot about the most important part of audio compression, the discrete cosine transform, also used in jpeg compression

[jayc]

Once again, great video! Thanks for sharing :)

[DeJayHank]

why were there no illustrations when he talked about the neighbouring frequency amplitudes and band filtering?

[MatkatMusic]

I hope you make a followup about Digital Video Compression!!

[JoelGarcia-mljx]

A Computerphile view of Opus Codec would be fantastic!!!

[solhsa]

hey, mod files aren't... uh.. well, close enough I guess

[cavalrycome]

The term 'audio compression' has different meanings for audio engineers and computer scientists so the title could be misleading and/or confusing for some.

[jurgentreep]

It was a bit short. I would have liked for him to go more in depth on the different rates of compression for different frequency ranges. Nonetheless still fun to watch :)

This video was VERY vague in information