Hi everyone, I'm new to this group and would like to ask a question. I've been working with TI's TMS320c32 for a class at my EE education, we've been mostly learning A/D and D/A converting and implementing FIR and IIR filters, but since it's getting so big I'm interested in the algorithms for modelling guitar amplifiers. Does anyone know some basics to how it's done? I suppose it's a bunch of fiters to get a desired frequency response, but it also needs some soft clipping and compression to emulate the analog (SS and vacuum tube) circuits behaviour. TIA /Johan
Amp modelling
Started by ●March 15, 2005
Reply by ●March 15, 20052005-03-15
in article kczZd.132506$dP1.471006@newsc.telia.net, Dope mcSmoke at dope@mc.smoke wrote on 03/15/2005 05:57:> Hi everyone, I'm new to this group and would like to ask a question. > > I've been working with TI's TMS320c32 for a class at my EE education, we've > been mostly learning A/D and D/A converting and implementing FIR and IIR > filters, but since it's getting so big I'm interested in the algorithms for > modelling guitar amplifiers. > > Does anyone know some basics to how it's done? I suppose it's a bunch of > fiters to get a desired frequency response, but it also needs some soft > clipping and compression to emulate the analog (SS and vacuum tube) circuits > behaviour.you have the right idea. modelling (and measuring) the non-linear behavior of a guitar amp is sorta difficult, otherwize more folks would be doing it. there are 2 companies, that i can think of that are into amp modelling, Sans Amp, and Line-6. maybe you can google around their keywords. also look at http://www.harmony-central.com/Effects/effects-explained.html i presume you know how to use a polynomial expression or table lookup to accomplish memoryless non-linear processing which might be part of this thing. one thing i should tell you is that, because non-linear operations increase bandwidth, you might have to upsample by a factor of 4 or 8 before doing any of this to avoid audible aliasing. that is computationally costly. at the end, you low-pass filter and then downsample back to your original. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●March 15, 20052005-03-15
robert bristow-johnson wrote:> in article kczZd.132506$dP1.471006@newsc.telia.net, Dope mcSmoke at > dope@mc.smoke wrote on 03/15/2005 05:57: > > >>Hi everyone, I'm new to this group and would like to ask a question. >> >>I've been working with TI's TMS320c32 for a class at my EE education, we've >>been mostly learning A/D and D/A converting and implementing FIR and IIR >>filters, but since it's getting so big I'm interested in the algorithms for >>modelling guitar amplifiers. >> >>Does anyone know some basics to how it's done? I suppose it's a bunch of >>fiters to get a desired frequency response, but it also needs some soft >>clipping and compression to emulate the analog (SS and vacuum tube) circuits >>behaviour. > > > you have the right idea. modelling (and measuring) the non-linear behavior > of a guitar amp is sorta difficult, otherwize more folks would be doing it. > there are 2 companies, that i can think of that are into amp modelling, Sans > Amp, and Line-6. maybe you can google around their keywords. also look at > > http://www.harmony-central.com/Effects/effects-explained.html > > i presume you know how to use a polynomial expression or table lookup to > accomplish memoryless non-linear processing which might be part of this > thing. > > one thing i should tell you is that, because non-linear operations increase > bandwidth, you might have to upsample by a factor of 4 or 8 before doing any > of this to avoid audible aliasing. that is computationally costly. at the > end, you low-pass filter and then downsample back to your original. >You may also want to do some web searches on the subject. Be aware that a digital guitar amp has been a goal for decades, but to date if you want that '60s sound you go get a Marshal or Fender amp -- in fact there's enough of a market tube equipment that all the pieces are available new, as well as brand new amps. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●March 15, 20052005-03-15
Tim Wescott wrote:> robert bristow-johnson wrote: > >> in article kczZd.132506$dP1.471006@newsc.telia.net, Dope mcSmoke at >> dope@mc.smoke wrote on 03/15/2005 05:57: >> >> >>> Hi everyone, I'm new to this group and would like to ask a question. >>> >>> I've been working with TI's TMS320c32 for a class at my EE education, >>> we've >>> been mostly learning A/D and D/A converting and implementing FIR and IIR >>> filters, but since it's getting so big I'm interested in the >>> algorithms for >>> modelling guitar amplifiers. >>> >>> Does anyone know some basics to how it's done? I suppose it's a bunch of >>> fiters to get a desired frequency response, but it also needs some soft >>> clipping and compression to emulate the analog (SS and vacuum tube) >>> circuits >>> behaviour. >> >> >> >> you have the right idea. modelling (and measuring) the non-linear >> behavior >> of a guitar amp is sorta difficult, otherwize more folks would be >> doing it. >> there are 2 companies, that i can think of that are into amp >> modelling, Sans >> Amp, and Line-6. maybe you can google around their keywords. also >> look at >> >> http://www.harmony-central.com/Effects/effects-explained.html >> >> i presume you know how to use a polynomial expression or table lookup to >> accomplish memoryless non-linear processing which might be part of this >> thing. >> >> one thing i should tell you is that, because non-linear operations >> increase >> bandwidth, you might have to upsample by a factor of 4 or 8 before >> doing any >> of this to avoid audible aliasing. that is computationally costly. >> at the >> end, you low-pass filter and then downsample back to your original. >> > You may also want to do some web searches on the subject. Be aware that > a digital guitar amp has been a goal for decades, but to date if you > want that '60s sound you go get a Marshal or Fender amp -- in fact > there's enough of a market tube equipment that all the pieces are > available new, as well as brand new amps. >I'm confused. I also have scar tissue on eardrum and partial nerve deafness due to infection. But just what is attraction of non-linear tube amps? Or Is it something I'm not equipped to appreciate - like shades to blind person?
Reply by ●March 15, 20052005-03-15
Richard Owlett wrote:> Tim Wescott wrote: > >> robert bristow-johnson wrote: >> >>> in article kczZd.132506$dP1.471006@newsc.telia.net, Dope mcSmoke at >>> dope@mc.smoke wrote on 03/15/2005 05:57: >>> >>> >>>> Hi everyone, I'm new to this group and would like to ask a question. >>>> >>>> I've been working with TI's TMS320c32 for a class at my EE >>>> education, we've >>>> been mostly learning A/D and D/A converting and implementing FIR and >>>> IIR >>>> filters, but since it's getting so big I'm interested in the >>>> algorithms for >>>> modelling guitar amplifiers. >>>> >>>> Does anyone know some basics to how it's done? I suppose it's a >>>> bunch of >>>> fiters to get a desired frequency response, but it also needs some soft >>>> clipping and compression to emulate the analog (SS and vacuum tube) >>>> circuits >>>> behaviour. >>> >>> >>> >>> >>> you have the right idea. modelling (and measuring) the non-linear >>> behavior >>> of a guitar amp is sorta difficult, otherwize more folks would be >>> doing it. >>> there are 2 companies, that i can think of that are into amp >>> modelling, Sans >>> Amp, and Line-6. maybe you can google around their keywords. also >>> look at >>> >>> http://www.harmony-central.com/Effects/effects-explained.html >>> >>> i presume you know how to use a polynomial expression or table lookup to >>> accomplish memoryless non-linear processing which might be part of this >>> thing. >>> >>> one thing i should tell you is that, because non-linear operations >>> increase >>> bandwidth, you might have to upsample by a factor of 4 or 8 before >>> doing any >>> of this to avoid audible aliasing. that is computationally costly. >>> at the >>> end, you low-pass filter and then downsample back to your original. >>> >> You may also want to do some web searches on the subject. Be aware >> that a digital guitar amp has been a goal for decades, but to date if >> you want that '60s sound you go get a Marshal or Fender amp -- in fact >> there's enough of a market tube equipment that all the pieces are >> available new, as well as brand new amps. >> > > > I'm confused. > I also have scar tissue on eardrum and partial nerve deafness due to > infection. > > But just what is attraction of non-linear tube amps? > Or Is it something I'm not equipped to appreciate - like shades to blind > person? > >The rock guitar sound has to go through a distortion to sound even remotely correct. An electric guitar played through a distortionless amplifier just sounds like your average classical guitar -- great if you want to play Segovia at high volume, or "Kumbaia", but abhorrently bad if you're aiming for "Smoke on the Water", "Stairway to Heaven", etc. The distortion effects are so heavy, in fact, that you have to adjust your playing to the amplifier - IIRC 3rds create nasty dissonances, but 4ths are the classic rock & roll "power chord". Tubes and output transformers, even power supply effects, all contribute to how a vacuum tube amplifier sounds. To date (AFAIK) the best that one can do to emulate the old amplifiers is to build a new amplifier _very_ carefully -- in fact there is one manufacturer that has stopped trying to do it with DSPs and is instead making an amp with various electronic switches to swap components in or out to modify the sound. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●March 15, 20052005-03-15
in article 113ec2c5902uo4d@corp.supernews.com, Richard Owlett at rowlett@atlascomm.net wrote on 03/15/2005 13:58:> I'm confused. > I also have scar tissue on eardrum and partial nerve deafness due to > infection. > > But just what is attraction of non-linear tube amps? > Or Is it something I'm not equipped to appreciate - like shades to blind > person?dunno, Richard. it depends on if you like electric guitar, and a little edge to that. one of the reasons for modeling this distortion is so that you don't have to crank your Marshall up to arc-weld (past "11" for you Spinal Tap freaks) thus bringing down your apartment building, just to get a good sounding electric guitar. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●March 15, 20052005-03-15
Tim Wescott wrote:> Richard Owlett wrote: > >> Tim Wescott wrote: >> >>> robert bristow-johnson wrote: >>> >>>> in article kczZd.132506$dP1.471006@newsc.telia.net, Dope mcSmoke at >>>> dope@mc.smoke wrote on 03/15/2005 05:57: >>>> >>>> >>>>> Hi everyone, I'm new to this group and would like to ask a question. >>>>> >>>>> I've been working with TI's TMS320c32 for a class at my EE >>>>> education, we've >>>>> been mostly learning A/D and D/A converting and implementing FIR >>>>> and IIR >>>>> filters, but since it's getting so big I'm interested in the >>>>> algorithms for >>>>> modelling guitar amplifiers. >>>>> >>>>> Does anyone know some basics to how it's done? I suppose it's a >>>>> bunch of >>>>> fiters to get a desired frequency response, but it also needs some >>>>> soft >>>>> clipping and compression to emulate the analog (SS and vacuum tube) >>>>> circuits >>>>> behaviour. >>>> >>>> >>>> >>>> >>>> >>>> you have the right idea. modelling (and measuring) the non-linear >>>> behavior >>>> of a guitar amp is sorta difficult, otherwize more folks would be >>>> doing it. >>>> there are 2 companies, that i can think of that are into amp >>>> modelling, Sans >>>> Amp, and Line-6. maybe you can google around their keywords. also >>>> look at >>>> >>>> http://www.harmony-central.com/Effects/effects-explained.html >>>> >>>> i presume you know how to use a polynomial expression or table >>>> lookup to >>>> accomplish memoryless non-linear processing which might be part of this >>>> thing. >>>> >>>> one thing i should tell you is that, because non-linear operations >>>> increase >>>> bandwidth, you might have to upsample by a factor of 4 or 8 before >>>> doing any >>>> of this to avoid audible aliasing. that is computationally costly. >>>> at the >>>> end, you low-pass filter and then downsample back to your original. >>>> >>> You may also want to do some web searches on the subject. Be aware >>> that a digital guitar amp has been a goal for decades, but to date if >>> you want that '60s sound you go get a Marshal or Fender amp -- in >>> fact there's enough of a market tube equipment that all the pieces >>> are available new, as well as brand new amps. >>> >> >> >> I'm confused. >> I also have scar tissue on eardrum and partial nerve deafness due to >> infection. >> >> But just what is attraction of non-linear tube amps? >> Or Is it something I'm not equipped to appreciate - like shades to >> blind person? >> >> > The rock guitar sound has to go through a distortion to sound even > remotely correct. An electric guitar played through a distortionless > amplifier just sounds like your average classical guitar -- great if you > want to play Segovia at high volume, or "Kumbaia", but abhorrently bad > if you're aiming for "Smoke on the Water", "Stairway to Heaven", etc. > The distortion effects are so heavy, in fact, that you have to adjust > your playing to the amplifier - IIRC 3rds create nasty dissonances, but > 4ths are the classic rock & roll "power chord". > > Tubes and output transformers, even power supply effects, all contribute > to how a vacuum tube amplifier sounds. To date (AFAIK) the best that > one can do to emulate the old amplifiers is to build a new amplifier > _very_ carefully -- in fact there is one manufacturer that has stopped > trying to do it with DSPs and is instead making an amp with various > electronic switches to swap components in or out to modify the sound. >Hmmmm. My tastes run towards "classical". Does that explain all ?
Reply by ●March 15, 20052005-03-15
"robert bristow-johnson" <rbj@audioimagination.com> wrote in message news:BE5CA0A7.5469%rbj@audioimagination.com...> in article 113ec2c5902uo4d@corp.supernews.com, Richard Owlett at > rowlett@atlascomm.net wrote on 03/15/2005 13:58: > > > I'm confused. > > I also have scar tissue on eardrum and partial nerve deafness due to > > infection. > > > > But just what is attraction of non-linear tube amps? > > Or Is it something I'm not equipped to appreciate - like shades to blind > > person? > > dunno, Richard. it depends on if you like electric guitar, and a little > edge to that. one of the reasons for modeling this distortion is so that > you don't have to crank your Marshall up to arc-weld (past "11" for you > Spinal Tap freaks) thus bringing down your apartment building, just to get a > good sounding electric guitar.One thing I've wondered, couldn't you insert an in-line attenuator between the power amp and the speaker(s), e.g. an "L-pad" or similar? That way you could still run your power tubes as hot as you want but be able to control the overall level. Or does that "mess up" the sound?
Reply by ●March 15, 20052005-03-15
Jon Harris wrote:> "robert bristow-johnson" <rbj@audioimagination.com> wrote in message > news:BE5CA0A7.5469%rbj@audioimagination.com... > >>in article 113ec2c5902uo4d@corp.supernews.com, Richard Owlett at >>rowlett@atlascomm.net wrote on 03/15/2005 13:58: >> >> >>>I'm confused. >>>I also have scar tissue on eardrum and partial nerve deafness due to >>>infection. >>> >>>But just what is attraction of non-linear tube amps? >>>Or Is it something I'm not equipped to appreciate - like shades to blind >>>person? >> >>dunno, Richard. it depends on if you like electric guitar, and a little >>edge to that. one of the reasons for modeling this distortion is so that >>you don't have to crank your Marshall up to arc-weld (past "11" for you >>Spinal Tap freaks) thus bringing down your apartment building, just to get a >>good sounding electric guitar. > > > One thing I've wondered, couldn't you insert an in-line attenuator between the > power amp and the speaker(s), e.g. an "L-pad" or similar? That way you could > still run your power tubes as hot as you want but be able to control the overall > level. Or does that "mess up" the sound?I tried that in self defense. It seems that the volume is an integral part of the experience. I've given up on discrete in-ear plugs. Now I wear big orange ear protectors to Bar Mitzvahs and youngster's weddings. Why pretend? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●March 15, 20052005-03-15
Jon Harris wrote:> "robert bristow-johnson" <rbj@audioimagination.com> wrote in message > news:BE5CA0A7.5469%rbj@audioimagination.com... > >>in article 113ec2c5902uo4d@corp.supernews.com, Richard Owlett at >>rowlett@atlascomm.net wrote on 03/15/2005 13:58: >> >> >>>I'm confused. >>>I also have scar tissue on eardrum and partial nerve deafness due to >>>infection. >>> >>>But just what is attraction of non-linear tube amps? >>>Or Is it something I'm not equipped to appreciate - like shades to blind >>>person? >> >>dunno, Richard. it depends on if you like electric guitar, and a little >>edge to that. one of the reasons for modeling this distortion is so that >>you don't have to crank your Marshall up to arc-weld (past "11" for you >>Spinal Tap freaks) thus bringing down your apartment building, just to get a >>good sounding electric guitar. > > > One thing I've wondered, couldn't you insert an in-line attenuator between the > power amp and the speaker(s), e.g. an "L-pad" or similar? That way you could > still run your power tubes as hot as you want but be able to control the overall > level. Or does that "mess up" the sound? > >I had an uncle who consulted with a rock band to do just that -- they ended up using heating elements from ovens for the pads, and everything worked just fine. You adjusted the tone with the gain control on the amp, and the volume with the pad. One of the fun parts is that uncle Coe was born in '31 or so, he was just a bit too old for rock and roll. Instead he was into organ music and barbershop quartets -- _not_ heavy metal rock. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
