Reversing Incoming Audio

[Kingston]

do NOT confuse the VST plugin buffers (host based) with any kind of look ahead buffering. It's (almost) a completely different thing.

You can already easily do "look ahead" buffers in synthmaker, or audio buffers in general. We already have that feature. What we do need is latency reporting to host, but I fear I'm already confusing you even further.

[skater130]

I just played around with the code from angstrom:
http://music-drive.com/rev_reverb.osm

BTW:
float mem[352800];// thats about 16 seconds at 120bpm.
has to be:
float mem[352800];// thats about 7 seconds at 44,1kHz samplerate.

I've been searching for hours for a practical example of exactly what I'm aiming to do, and this is it!...except the file is no longer active. If you happened to have a copy MyCo or can explain the inner workings of reversing audio (which can't be done on the fly due to latency - I guess the unprocessed signal can be delayed in order to wait for it to catch up?) It would be deeply appreciated.

(EDIT: Sorry for re-igniting an old thread...hopefully there's still people out there in the know!)

[trogluddite]

Here's a little module that can do the reversing - it's really meant as a pitch shifter (from the algorithm posted HERE), but the same method has the ability to reverse its input buffer, and has crossfades to avoid any nasty clicking.

Pitch and Reverse.osm

(6.26 KiB) Downloaded 213 times

The 'Window Size' parameter in the properties sets the size of the buffer (and hence the latency).

[Leslie147]

Trogluddite, thank you very much for sharing that module. I appreciate it was quite a while ago that you posted the .osm file but I hope this gets back to you.

The way you create the slopes is a lesson in compact code writing but I haven't yet managed to figure out the function of absmask=2147483647. Your advice on this would be much appreciated.

When I tried to use the shifter fourfold I spotted 'temping[1]' instead of tempind[1] in writing to the array which prevented one channel from working. Also, I noticed the window size is limited to 1 second by the Float Min 44100 even though the array is sized for a maximum of 10 seconds. Fixing this, I found a 2 second window very musical.

Having deduced and written out the mathematical basis for the way this works, I can see how you reverse time by effectively swapping the sign of t in sinw(t+T) ... given an input signal sinwt. Brilliant! The Vox Tonelab pedal board I have does a time reverse that sounds similar to this but it's good to have it in a form that can be manipulated freely.

Thanks again,

Chris

[trogluddite]

No problem - I can't really take all the credit anyway, as the code was an my assembly optimisation, of another guys code, who ported an algorithm....

The ABSmask is just a very fast way to create the ABS(x) function - the integer has the lowest 31 bits all set to one, and the 32nd bit (sign bit) set to zero.
Because float numbers also use the top bit as the sign bit, when you do a bitwise ANS with any 32bit number, the sign bit will be masked out - turning negative numbers into positive ones.