Dithering to 16bit. Can you hear it?

Over at recordingreview.com I made the comment I could hear the difference between 24 bit dithered and non-dithered to 16 bit. I got called on it, “I’d like to see you pick it out double blind”. I felt the same way so I set up a semi-scientific test. Here she is with my findings.

Summery: You can hear the difference. It’s super subtle and not worth much concern. But there is no reason not to dither down to 16 bit. So why not do it?

Here are the samples. Listen for yourself. My understanding is SoundCloud plays back as MP3s but if you download you get the original file. The original is a wav at 16bit/48k.

No dither by cporro

Dither by cporro

I used a Shure KSM44 mic to record various drum hits on my acoustic kit. Recording was done at 24bit/48k. The sample I chose for the test is just a few snare hits. I exported the audio raw from Samplitude. One export was dithered using Samplitude’s triangular dither. The other was not dithered. Both exports were at 16bit/48k.

I then bought them back in the original recording session (actually the exports were set up to go directly into the Samplitude project). I toggled back and forth between dithered and undithered. The dithered sample had fuller sounding snare hits. It also sounded less harsh.

But doing a blind test inside samplitude is a pain. You need to close your eyes, toggle the samples around enough so you have no clue which one you are hearing, make your decision, open your eyes, and then log the results.

So I used Foobar with the ABX Comparator component. This allows you to do easy blind testing. And how did this go? Not so well. I wish there was more documentation on this component because I had a hard time  interpreting it’s results. For example it calculates the chance you are guessing but that stat never added up for me. I did 40 trials where I just guessed and that stat never got close to 100%.

In my trials for picking out dither with ABX Comparator I did skew towards not guessing. But it was not the concrete case I expected. I really had to listen hard and sometimes I wasn’t right.

Back to Samplitude where things get strange.  Again I am able to pick out the dither with 100% accuracy. I must have done 30 trials this way. The chances of guessing correctly 30 times is extremely low. Someone who remembers probability chime in.

Inside Samp I decided to do a null test to see what the actual difference was between the dithered and undithered versions. The noise was below -80db. I certainly could not hear that.

So what is going on? All I can figure is Samplitude is playing back the audio differently then Foobar.  If this it true it’s kind of a shame because I was really looking forward to having something like ABX Comparator for blind tests. Wah!

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