[linux-audio-dev] [ann] unmatched - a LADSPA amp tone

[Tim Goetze]

Steve Harris wrote:

>On Thu, Oct 24, 2002 at 01:19:20 +0200, Tim Goetze wrote:
>> >I'm 90% sure its from the crossover between the two halves of the class B
>> >amp (thats the power amp IIRC).
>> 
>> drat. i wish i was better at understanding electronics.
>> the amp guy pointed in this direction too.
>
>Did he give the impression that he though it was an important part of the
>sound? I'm not clear on this.

unfortunately he didn't have the time to give more than
a few hints, which mostly covered electronic, not sonic
aspects. what i got out of it basically explains the
scope shots paul has thrown in.

>> the aliasing is not that strong, you're right. maybe i'm
>> over-sensitive.
>
>No, no. Aliasing really ruins analogue effects IMHO. On Friday and/or over
>the weekend I'm dig out my bass and try it.

make sure you try the iir 'convolver' with the bass. i
like the combination a lot.

>> we'll need for the real rough tone -- we'll have to come up 
>> with a bandlimited solution. the current valve clipping is 
>> real soft compared to those scope shots, isn't it? if we
>> stack the valve to get to hard clipping, the net result will 
>> carry the sum of all aliasing i'm afraid.
>
>Yes, it will compund it. I can't think how to apply oscillator
>antialiasing to wavewhaping though. Maybe it can be done.

for square clipping, i'm thinking about interpolating where
the input will hit the limit, giving us a sub-sample point
in time, on which one'd center the sinc. the quality of the
clipping point interpolation would be crucial. if this 
works for square clipping, moving the clipping level and
blending with the straight signal might work to produce
a smooth range of clipping. still needs more thinking though.
 
>> my feeling is that oversampling alone will not do, although
>> you're probably right in that it will get rid of most of 
>> the aliasing. 
>
>Its how most people tackle to problem. I think I can get the valve cheap
>enough that it will be practical.

that'd be great.
 
>I doubt that the electronics ever produces hard square clips.

don't the scope traces suggest they do? i'll try and record
the circuit output from the fender, it has line-out and fx 
send.

tim