A few posters indicated some interest in the progress of this SW project so I thought I'd post an update here.
Work has begun (mainly GUI and internal architecture at this point) and I've set-up a sourceforge page for the project. I've decided to called it Stomper. Here's a link (with a couple of early screenshots!):
https://sourceforge.net/projects/stomper/
Please feel free to share your thoughts and suggestions (here or on sourceforge).
seeking HW advice for new SW project
Moderators: MattKingUSA, khz
-
folderol
- Established Member
- Posts: 2082
- Joined: Mon Sep 28, 2015 8:06 pm
- Location: Here, of course!
- Has thanked: 227 times
- Been thanked: 400 times
- Contact:
Re: seeking HW advice for new SW project
Just a few notes on the hardware side.
In general, for impedance you want to go low to high so a 10k ohm output into a 100k input is fine. The other way round might be a problem. This is especially true of passive pickups which is why guitar amp inputs are usually around 1Meg. Special cases are some dynamic mics and and speakers on valve amps. Valve amps can be damaged if the speaker impedance is higher than the stated value, or becomes disconnected.
Levels. Instrument inputs are generally around 50-100mV. Line levels anything from 250mV to 2V! If you are feeding the interface lineout into an instrument input of the amp you might be overloading it. In this case you need an attenuator. This can simply be 2 resistors - google is your friend
DI boxes can be helpful if you're getting hum problems (earth loops) but other than that I would think them unlikely to be of benefit in your case.
I'm not sure exactly what you expect to get from the amp (and I don't know your one). In most situations I've heard of it is to get the amp's driven characteristics. The sound that defines an amp is usually created by its output stage and/or cone breakup of the speaker. Amp line outs don't commonly come that late in the chain. and for cone breakup the only solution is a mic on the speaker!
Hope some of that help.
In general, for impedance you want to go low to high so a 10k ohm output into a 100k input is fine. The other way round might be a problem. This is especially true of passive pickups which is why guitar amp inputs are usually around 1Meg. Special cases are some dynamic mics and and speakers on valve amps. Valve amps can be damaged if the speaker impedance is higher than the stated value, or becomes disconnected.
Levels. Instrument inputs are generally around 50-100mV. Line levels anything from 250mV to 2V! If you are feeding the interface lineout into an instrument input of the amp you might be overloading it. In this case you need an attenuator. This can simply be 2 resistors - google is your friend
DI boxes can be helpful if you're getting hum problems (earth loops) but other than that I would think them unlikely to be of benefit in your case.
I'm not sure exactly what you expect to get from the amp (and I don't know your one). In most situations I've heard of it is to get the amp's driven characteristics. The sound that defines an amp is usually created by its output stage and/or cone breakup of the speaker. Amp line outs don't commonly come that late in the chain. and for cone breakup the only solution is a mic on the speaker!
Hope some of that help.
The Yoshimi guy {apparently now an 'elderly'}
Re: seeking HW advice for new SW project
Hi there! I have just skimmed through the thread, so I didn't read everything carefully, but I hope I will be useful for you.
On the hardware side: all audio circuits use voltage signals. Good coupling of circuits (and then good signal transfer) happens when coupling a low output impedance circuit with a high input impedance circuit. The mentioned solutions (DI box, switchblade, buffered stompbox...) would work. Alternatively, with few bucks, you can build a very simple buffer yourself. Buy an opamp of the TL08X series: they are very good for audio applications (I have used them extensively for my guitar stompboxes designs). The last digits says to you how many opamps in the package. Then, you can design a simple opamp buffer. The very simple scheme on wikipedia works already well (I am using it extensively in an analog envelope filter design I am completing... very slowly). However, you should be able to find examples online and in the datasheets. Then you will need some components to build a virtual ground and some capacitor. Maybe you can add an input capacitor to make sure to block DC, but beware that this will change the input impedance, which is greatest injecting the signal in the opamp directly. I think you can avoid the input capacitor since the DC will be decoupled at the soundcard output. If you want to use capacitor maybe an emitter follower setup is better, but more complex. Use film capacitors for proper audio performances, like these, if you put a capacitor in the audio signal path. That's all. According to my experience you should be able to be done with few euros. The buffers inside stompboxes are usually made like that. If you have a boss pedal you can use it turned off, they should have a never bypassed opamp buffer inside.
As for the soundcard, I own a Scarlett 2i4 that has midi connectivity and excellent Linux compatibility. I judge it overpriced for the performances though... I made some point here and here.
On the hardware side: all audio circuits use voltage signals. Good coupling of circuits (and then good signal transfer) happens when coupling a low output impedance circuit with a high input impedance circuit. The mentioned solutions (DI box, switchblade, buffered stompbox...) would work. Alternatively, with few bucks, you can build a very simple buffer yourself. Buy an opamp of the TL08X series: they are very good for audio applications (I have used them extensively for my guitar stompboxes designs). The last digits says to you how many opamps in the package. Then, you can design a simple opamp buffer. The very simple scheme on wikipedia works already well (I am using it extensively in an analog envelope filter design I am completing... very slowly). However, you should be able to find examples online and in the datasheets. Then you will need some components to build a virtual ground and some capacitor. Maybe you can add an input capacitor to make sure to block DC, but beware that this will change the input impedance, which is greatest injecting the signal in the opamp directly. I think you can avoid the input capacitor since the DC will be decoupled at the soundcard output. If you want to use capacitor maybe an emitter follower setup is better, but more complex. Use film capacitors for proper audio performances, like these, if you put a capacitor in the audio signal path. That's all. According to my experience you should be able to be done with few euros. The buffers inside stompboxes are usually made like that. If you have a boss pedal you can use it turned off, they should have a never bypassed opamp buffer inside.
As for the soundcard, I own a Scarlett 2i4 that has midi connectivity and excellent Linux compatibility. I judge it overpriced for the performances though... I made some point here and here.
Last edited by CrocoDuck on Mon Oct 12, 2015 12:10 pm, edited 3 times in total.
-
asbak
- Established Member
- Posts: 897
- Joined: Thu Sep 11, 2014 3:04 pm
- Has thanked: 71 times
- Been thanked: 64 times
Re: seeking HW advice for new SW project
I would search the ALSA hardware compatibility and related pages listing supported audio interfaces or search the forums for interfaces already reported to-be-working under Linux instead of compiling Amazon listings. Typical fare on Amazon assumes Windows and Mac, not Linux users.raybert wrote:Thanks again for all the input everyone.
I've decided to buy a new audio interface for this project, one that also supports midi (my Scarlett doesn't) so I can minimize the number of devices I need to have on stage. I'm wondering if anyone has any suggestions.
I made a (sorta) quick scan of devices on Amazon the other day; these are the ones that made my short list:
It may also be worth checking which devices are USB Class Compliant because theoretically they should work under LInux.
Some Focal / 20.04 audio packages and resources https://midistudio.groups.io/g/linuxaudio
Re: seeking HW advice for new SW project
On Amazon, I like to jump to the comments/reviews and look for "Linux" from the search box. It really works, it will find the word if it's there. You can find the odd Linux warrior reporting his degree of success with the item.