Reversing Incoming Audio

[Tom7777]

Since im no coder i havent really been using the audio buffer modules which i know its possible to reverse samples but how would i reverse a stereo audio signal? thanks

[Shifrin]

AFAIK you couldn't, if you literally mean you want to reverse an audio input in realtime it's not possible. Think of it this way, say you have a wave file and reverse it, the end becomes the start. You couldn't do this in realtime because you need all the sample data to perform the operation, but you only get a sample at a time from the start. You could write something to read into a buffer and then reverse the buffer as output, this would have a delay equal to the size of the buffer and play 'chunks' of audio in reverse. You could also write a delay effect that plays the delayed signal in reverse too

I'd love to know if there's a magical way to do what you want

Shif.

[Tom7777]

You could write something to read into a buffer and then reverse the buffer as output

Yeah this is the type of thing i wanted to know how to do, i know that realtime reversing is not really possible, I was thinking about making a reversed delay actually but im confused as to how i would go about doing so.

[rullyastronout]

i think vst system, has a block of sample given depend on souncard latency setting, before we can start the process.
so we actually can reverse the sample between a block of samples, but i don't know how to do it in sm. in c++ you could.

i hope there some one can tell me how to
==>get ablock of sample
==>process it
==>send out at no delay.

[angstrom]

depends if you want any pitch bending or not .. to get a scratch effect. In which case there was a nice scratch sequencing thing posted a while back - or sambean posted a record stop effect (I think it was sam anyway). I mention those because you will need to take a look at their interpolation.

basically, for a simple reverse you should define a block of memory as long as you think you will need and add samples to it like a delay buffer

float mem[352800];// thats about 16 seconds at 120bpm.
mem[index] = in;
index = index + 1;

stop counting when you run out of buffer or when it's time to reverse. Then, do something like

index = index-1;
out = mem[index];

that's roughly it anyway. Start with a basic delay and go from there. Try it , it's fun to make the code window crash

[MyCo]

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.

[Tom7777]

Your link doesn't seem to be working MyCo

[angstrom]

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

I had a delay OSM open at the time I posted - which has a GUI button for 16 seconds, but I hadn't actually made the code capable of that. I should have noticed really as 352,800 / 44,100 = 8

Anyway. 8 seconds is a pretty healthy buffer.

[MyCo]

Your link doesn't seem to be working MyCo

Server is down, try again in some hours.

[Tom7777]

Ok thanks MyCo

[Tom7777]

It's working now

[Kingston]

i think vst system, has a block of sample given depend on souncard latency setting, before we can start the process.
so we actually can reverse the sample between a block of samples, but i don't know how to do it in sm. in c++ you could.

i hope there some one can tell me how to
==>get ablock of sample
==>process it
==>send out at no delay.

That's not what the internal processing blocks (ie the buffer) in VST host does. That's for the hosts internal processing method only.

Basically any effect needs its own buffer where you can store an arbitrary lenght of audio (to be reversed or whatever). This will automatically generate a latency also, and there's just no way around that. We just can't see in the future.

Luckily, if the effect has a "look ahead buffer" like this we could report that to the host which can then (if supported) compensate for it.

Unfortunately there's no way to report the latency of SM plugin to the host.

That feature is high on my wish list.

[MyCo]

It's working now

just wanted to say that now... but you were faster.

[Tom7777]

[rullyastronout]

Code: Select all

Luckily, if the effect has a "look ahead buffer" like this we could report that to the host which can then (if supported) compensate for it.

Unfortunately there's no way to report the latency of SM plugin to the host.

That feature is high on my wish list.

o well, look ahead buffer, thats exacly what i mean. so i'll be the second person who put the wish list on top, thanks for info kings.
and how about this, does this also called look ahead buffer...

Code: Select all

void AGain::processReplacing (float **inputs, float **outputs, long sampleFrames)
{
    float *in1  =  inputs[0];
    float *in2  =  inputs[1];
    float *out1 = outputs[0];
    float *out2 = outputs[1];
    int index=0;

    while (--sampleFrames >= 0)//depend on sampleframe given
                                              //the look ahead buffer
    {
          while(index!=100)
          {
          index=index++;
          float Left[index] = *in1++;
          }
//and so on