I recently recorded an impulse response of the reverb of a 14th-century church (more or less the footprint of the sound ambiance of the building). Here is how I did it.
- First I installed a loudspeaker (a studio monitor Yamaha HS-80M) in the church, quite high from the ground. I played, rather loud, a sound called a frequency sweep, that contains frequencies from 20Hz to 20000Hz, i.e. the entire human hearing range.
- Then, in the middle of the church, I recorded this with 2 microphones. Here is what I got:
Quite a lot of reverb, that's exactly what we want to catch with an IR!
Now, let's use some Digital Signal Processing to get the IR. All the source code in Python is here. If you're into math, here is the idea:
ais the input sweep signal,
hthe impulse response, and
bthe microphone-recorded signal. We have
a * h = b(convolution here!). Let's take the discrete Fourier transform, we have
fft(a) * fft(h) = fft(b), then
h = ifft(fft(b) / fft(a)).
- Here is the result, the Impulse Response of the church:
Then, of course, we can do some cleaning, fade out, etc.
But what is this useful for? You can use this Impulse Response in any music production software (the VST SIR1 is quite good and freeware) , and make any of your recordings (voice, instrument, etc.) sound like if they were recorded in this church. This is the magic of convolution reverb!
Useful trick when you record your own IR: play
sweep0.wav in the building instead of
sweep.wav. The initial "beep" is helpful to see exactly where things begin. If you don't do that, as the sweep begins with very low frequencies (starting from 20 Hz), you won't know exactly where is the beginning of your microphone-recording. Once your recording is done, you can trim the soundfile by making it begin exactly 10 seconds after the short beep.
I don't share Jeff Atwood's enthusiasm about HTTPS / encryption. What will happen if HTTPS becomes the standard and if HTTP is considered by browsers as "unsafe"?
It seems to me that then, the web will be separated in 2 worlds: professional websites who can afford SSL certificates and a dedicated team to maintain the certification process ... and the average small webmaster who just has a shared hosting and a Wordpress. The latter will be slowly "pushed out of internet" with the threatening notice
Even with the free Let's Encrypt initiative, maintaining HTTPS requires technicity, much more than what the average webmaster has.
Result: if HTTPS becomes the standard and normal HTTP is alerted by browsers as unsafe by default, this will slowly kill amateur content, citizen-powered content.
Welcome to even-more centralized internet. Be sure Facebook and other big content providers will like this.
Many things begin with
Let's start a new notebook!
(Well sometimes the notebook is abandoned after 3 pages, but hmm, let's not think about it). Writing helps to know what you want, what you don't want, and what you've done so far. So I decided
Let's start a blog!
Then I looked at many blog generator tools, and noticed it would be faster to actually write it myself in PHP, rather than downloading every existing solution and pick the best (so hard to make a choice). So I started yesterday evening, and today it's done: