TOPIC: IRs length

IRs length 8 years 1 month ago #7935

Now that the convolver is able to load impulses of any size, I was able to use normal length ownhammer IRs into it (for this reason, and for the benefits of the interface and filters now available in pro convolver, I dismissed redwirez mixIR2).
I use OH impulses as well as the ones built in s-gear, especially the Scuffham made are really outstanding.
Now, I noticed loading two OH IRs into the convolver almost DOUBLED the CPU usage. Since I know that the more the IRs length the more the CPU consumption, I switched to the truncated versions.
Result: CPU usage dropped dramatically and I was not able to hear any differences between normal length and truncated versions. I A/Bed the two for an hour, with high quality monitoring headphones, at all volumes, all kind of sounds.... No difference at all, to my ears.

So I must assume IRs length, at least at some extent, does not affect cab convolution quality. Am I right? If this is true, it is a nonsense using really long IRs, when you can save horsepower for other stuff.

Any thoughts? Maybe a technical explanation could help... Mike, what do you think about this?
Last edit: 8 years 1 month ago by mike. Reason: typo in topic subject
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IRs lenght 8 years 1 month ago #7937

the lengthier IRs is just repeating the same thing than shorter, it won´t add anything to the existing sound.
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IRs lenght 8 years 1 month ago #7941

Not really. IRs are wav files, containing a sound wave made by a certain number of samples at a certain resolution. So, they have a transient and a tail: the longer the impulse, the longer the tail.
Try opening one in a daw and you will see it clearly. The matter is if the 'information' contained in the tail is needed for reproducing all the low frequencies of a specific cab. That is to say, if 'truncating' or capturing a limited number of samples can really capture all the information about lower frequencies of the cab/mic/preamp/room.
OwnHammer truncated IRs, at 44.1KHz, contain 8820 samples and are 220ms long, which seems quite a LOT...

There is a very interesting wiki article with considerations from Cliff at Fractal Audio, here .
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IRs length 8 years 1 month ago #7954

This came up recently in another thread .

Here are some pointers:

Too short an impulse may impact the low frequency accuracy:
If the impulse is very short (i.e. less than 5000 samples at 44.1 KHz samplerate) then you might be losing some accuracy in the low frequencies. Whether or not this matters is subjective from impulse to impulse. Most (probably all) convolver implementations use a mathematical 'FFT' or Fast Fourier Transform. This technique takes a time domain impulse and transforms it into the frequency domain where it is applied to the signal (also transformed into the frequency domain). If the FFT length is short, then the frequency 'buckets' become more course at lower frequencies, hence you may see inaccuracy at lower frequencies in the resulting frequency response. Note that the higher the sample rate, the more pronounced the effect. Through experimentation, I've found that at 44.1KHz sample rate, an impulse of 5000 samples or greater is usually enough to minimise any inaccuracies.

The S-GEAR Scuffham impulses are between 6000 and 9000 samples in length at 44.1 sample rate. At higher sample rates the impulses are longer. In fact the impulses are are probably a bit longer than they need to be.

How much room response is captured in the impulse?
In the earlier thread I mentioned that the appropriate length of an impulse can depend on how much of the room has been captured in the impulse, and how much or that effect you want in the resulting signal.
The most common measurement technique is to run an exponential sine sweep through the system under test and deconvolve the result with the inverse filter. This method does not attempt to separate the room response from the equipment response. You will capture both time domain effects (reflections and echoes) and frequency domain effects (frequency response and frequency-dependent reverberation). Truncating the impulse will remove some of the time domain effects of the room.

If the impulse was captured with no room effects, then you might summise that the maximum required IR length might be about 2200 samples (at 44.1) to capture frequencies down to 20Hz. However, given the short impulses issue described above, you may hear a significant difference between the 2200 and the 5000 sample impulses. In reality, most impulses have are not totally free of room effects, so they may have a somewhat longer tail anyway.

The Scuffham impulses in S-GEAR were recorded in an acoustically treated professional studio - one with a pleasantly damped sound. I didn't truncate the tails.

Also, note that the ProConvolver MKII allows you to import any length IR, but still truncates impulses internally to a maximum of 20,000 samples. More than enough for any cabinet response.

I hope the above info helps.

Mike
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Last edit: 8 years 1 month ago by mike.
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IRs length 8 years 1 month ago #7958

Mike, this is really useful, thank you.

Definitely, what you are saying strengthen my first impression. With the new version of s-gear I am keen to use stock IRs a lot more, and some OH, like the wonderful (to me) 2x12 D120 and 4x12 Scumback.
Being the truncated OH version 8820 samples, and 220 ms long, there is no real information loss, cause the truncated stuff is just silence, and this saves me lots of CPU.

Btw, I hope you will soon make some 2x12 and 4x12 impulses, the 1x12 you included in S-gear are just sweet, they seem to fit just perfectly with many tones
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IRs length 8 years 1 month ago #7977

I´ve downloaded some free IRs from "The AmpFatory" to check them out but unfortunatly they don´t load into S-Gear´s convolver.

If anybody will try here´s the link

www.theampfactory.com/free-stuff/
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IRs length 8 years 1 month ago #7989

Redwirez seem to be 2kb to 12kb for 44.1 24 bit. Others free on web seem to be 800b to 12kb that I have used and work.

Another question I would have is that some cab impulses tend to work better with distortion/gain models rather than clean. I.e., I can hear more of a difference when used with some distortion on guitar/gain.
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IRs length 8 years 1 month ago #8122

javi wrote:

I´ve downloaded some free IRs from "The AmpFatory" to check them out but unfortunatly they don´t load into S-Gear´s convolver.

If anybody will try here´s the link

www.theampfactory.com/free-stuff/

I just had an exchange with Andy from theampfactory. He can't load them either.

MIKE, can you check the above link, download the free IR's and test out why these are not loading into S-gear ? It does not seem to recognize them. Andy's work is great and I would really like to use his IR's .

Thanks ! :)
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IRs length 8 years 1 month ago #8123

Jerryratpack wrote:

javi wrote:

I´ve downloaded some free IRs from "The AmpFatory" to check them out but unfortunatly they don´t load into S-Gear´s convolver.

If anybody will try here´s the link

www.theampfactory.com/free-stuff/

I just had an exchange with Andy from theampfactory. He can't load them either.

MIKE, can you check the above link, download the free IR's and test out why these are not loading into S-gear ? It does not seem to recognize them. Andy's work is great and I would really like to use his IR's .

Thanks ! :)

Does S-Gear give you an error message after import? Or will it not even allow you to select those IRs?
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IRs length 8 years 1 month ago #8126

elambo wrote:

Does S-Gear give you an error message after import? Or will it not even allow you to select those IRs?

It doesn't recognize the format as a +.wav, that's the error message:


HTH,
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IRs length 8 years 1 month ago #8127

I thought perhaps the filename lacked the .wav extension but there it is plain as day. Guess that one will have to wait for Mike.
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IRs length 8 years 1 month ago #8131

LtKojak wrote:

elambo wrote:

Does S-Gear give you an error message after import? Or will it not even allow you to select those IRs?

It doesn't recognize the format as a +.wav, that's the error message:


HTH,

I have those same IR's . I couldn't remember where I got them from, and then as I was looking at this thread, I remembered the truncated versions of ownhammer I have . I guess most s gear users downloaded those.

Anyway, thanks for posting the screenshot . Hopefully Mike will have a fix
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IRs length 8 years 1 month ago #8132

Downloaded the ampfactory stuff, but if I remember correctly I had to convert them for some reason. I used format factory to do it and it took about 10 sec. They're working fine now.
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IRs length 8 years 1 month ago #8133

Chan wrote:

Downloaded the ampfactory stuff, but if I remember correctly I had to convert them for some reason. I used format factory to do it and it took about 10 sec. They're working fine now.
As I use Format factory to convert Video formats to watch with my DVD player, out of curiosity I just did this and now they load and work OK. Problem solved! ;)

HTH,
Last edit: 8 years 1 month ago by LtKojak.
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IRs length 8 years 1 month ago #8134

Ok great ! I will check out "format factory" .

Thanks gents !
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IRs length 8 years 1 month ago #8136

LtKojak wrote:

Chan wrote:

Downloaded the ampfactory stuff, but if I remember correctly I had to convert them for some reason. I used format factory to do it and it took about 10 sec. They're working fine now.
As I use Format factory to convert Video formats to watch with my DVD player, out of curiosity I just did this and now they load and work OK. Problem solved! ;)

HTH,

I downloaded the format program, and converted the select files to wav , but when I drag them in the s gear folder, they show up, but there is no output. No sound at all and no levels on the output.
Is there a step I am missing ? Thanks,
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IRs length 8 years 1 month ago #8141

Jerryratpack wrote:

converted the select files to wav , but when I drag them in the s gear folder, they show up, but there is no output. No sound at all and no levels on the output.
Is there a step I am missing ? Thanks,

Well, I went back and found that the converted .wav files will load but won't produce a sound that's loud enough to be usable, not even normalizing'em with Audacity. I would've swear that yesterday they worked, but obviously I was mistaken and I'm sorry for that.

Having said that, in my case, although I own many IRs from Ownhammer, Redwirez and others, I've found myself using the Scuffham IRs, specially the S12L, the S12-65 and the British Blue the most, after upgrading to v. 2.42. Specially the S12L gives me the cleans no other commercial IR in the market do.

HTH,
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IRs length 8 years 1 month ago #8147

LtKojak wrote:

Jerryratpack wrote:

converted the select files to wav , but when I drag them in the s gear folder, they show up, but there is no output. No sound at all and no levels on the output.
Is there a step I am missing ? Thanks,

Well, I went back and found that the converted .wav files will load but won't produce a sound that's loud enough to be usable, not even normalizing'em with Audacity. I would've swear that yesterday they worked, but obviously I was mistaken and I'm sorry for that.

Having said that, in my case, although I own many IRs from Ownhammer, Redwirez and others, I've found myself using the Scuffham IRs, specially the S12L, the S12-65 and the British Blue the most, after upgrading to v. 2.42. Specially the S12L gives me the cleans no other commercial IR in the market do.

HTH,

Hey LT , no problem at all. I ended up leaving it be. I started to have all sorts of issues with Amplitube and revalver , and I thought it was from the format factory I downloaded, so I deleted that program first... I now believe it was either my windows security update causing issues. In either case, I appreciate the info you share, and it was worth a try.
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