Serial or Parallel Effects

[talltxguy]

I spoke with Mike at Mesa today, and he said he was pretty sure the Studio Pre had a serial effects loop. Anybody know for sure?

While we're on effects loops, what about the Triaxis? It is parallel or series?

My concern is running digital rack effects with a parallel loop. From what I've read, that can cause some issues. However, those same kinds of issues weren't mentioned when running analog stomps.

Thanks for any insight,
Scott

 

[ando]

Triaxis is a serial loop. Don't know anything about the Studio Pre.

Some digital processors can have phase issues when using parallel loops - produces odd filtering effects and canceling of certain frequencies. Even so, it is a rare thing. I wish the Triaxis had a parallel loop because I like to hear a mostly plain tube tone with a splash of effects over it. When you use a digital processor in a serial loop, the entire signal is passed through two conversion processors A->D then D->A. Not quite as pure as keeping the original tone.

 

[talltxguy]

Ando and others,

I've got an analog pedal that has a MIX function on it so that I can control the amount of effect. Do the any of the digital rack devices have a similar thing going on?

Sounds like you're saying that it does not even matter because even with say a 10% mix of effect, you're still having your signal turned to digital and back again...right?

I'm a bit concerned about having the signal go to digital and back again. Is there a spec number on the digital processors that makes the signal sound...less digital? LoL What I mean is this: does a processor with a 96 kHZ sampling rate sound less digital than one with 44.1? Or is it the digital conversion? Whether it's high end Lexicons or an Eventide H8000, the highest AD to DA conversion seems to be the same conversion I can get on a $200 Lexicon MX200 - 24-bit processing. I did notice that those high end processors do have dynamic ranges around 110 to 112 compared to 107dB of the MX200. Lexicon also advertises a 32/64 bit floating point internal audio DSP, a stat I didn't see mentioned on the Eventide merchandise.

Ando, have you thought about running 2 Triaxes at the same time? One dry and one wet? Assuming you had the $ to fund it, would that be a possibility?

 

[ando]

Ando and others,

I've got an analog pedal that has a MIX function on it so that I can control the amount of effect. Do the any of the digital rack devices have a similar thing going on?

Sounds like you're saying that it does not even matter because even with say a 10% mix of effect, you're still having your signal turned to digital and back again...right?

I'm a bit concerned about having the signal go to digital and back again. Is there a spec number on the digital processors that makes the signal sound...less digital? LoL What I mean is this: does a processor with a 96 kHZ sampling rate sound less digital than one with 44.1? Or is it the digital conversion? Whether it's high end Lexicons or an Eventide H8000, the highest AD to DA conversion seems to be the same conversion I can get on a $200 Lexicon MX200 - 24-bit processing. I did notice that those high end processors do have dynamic ranges around 110 to 112 compared to 107dB of the MX200. Lexicon also advertises a 32/64 bit floating point internal audio DSP, a stat I didn't see mentioned on the Eventide merchandise.

Ando, have you thought about running 2 Triaxes at the same time? One dry and one wet? Assuming you had the $ to fund it, would that be a possibility?

You have a pretty decent understanding of the issues. Yes, the higher the sampling rate and the higher the quantization (number of bits) the less digital it will sound. But that's only part of the story. If you get a high quality effects unit, the reality is it shouldn't sound too digital anyway. It's more of an issue for lower end digital processors. Because in a serial loop, everything will go through conversion, it's all the more important that you use a high quality processor. That way, the mix, as well as the quality of the effects, will undergo less degradation. I use a TC G Major 2, which is a medium quality processor, and it's acceptable in terms of sound quality. I think the main reason I prefer parallel loops is because there is no latency on the dry portion of the signal. When going serial, there is a tiny latency, even if it's only 1 or 2 milliseconds, which makes you feel just slightly less connected to your sound and movements. For most people that will never be an issue - after all, latency is present even if you move a few extra steps from your amp. I guess it's the cumulative effect of the latencies.

None of the digital FX I've seen have an analog mix function - that's a lot harder to do when you are talking about a device that stores presets (and wet/dry mixes) digitally. Keeping it all digital within the unit also helps to avoid the phasing issues I outlined above.

In any case, as it stands, I don't plan to run a setup that is any more complex than what I have so I will just put up with the serial loop, which when all is said and done, works quite fine. I wouldn't want an extra Triaxis or more cabinets - I prefer having a compact rack that does whatever I want it to with minimal fuss. I'm happy enough. I also know that I am the type of person who will never be 100% happy with any amp I have so I have to learn to be satisfied with slightly less! I can say that I am happier with my current setup than any previous setup so that's not bad. There have been a couple of MIDI controllable line mixers which would achieve what I want in terms of a parallel loop, but they don't seem to be made anymore. The Marshall JMP 1 also has a parallel loop which is excellent, but Mesa went another way unfortunately. Just another example of how differently everybody sees technology.

To finish, I wouldn't worry so much about what the technical specs say, I would use the effects that sound the most pleasant to your ear because there is tone shaping going in there as well as the raw processing aspect of A/D conversion. Sometimes you will be more pleased by units which you can't just justify in terms of technical superiority.

 

[elvis]

The studio pre is a series FX loop.

Whatever you believe about parallel vs. series, a major problem with parallel FX loops and digital FX is latency. Digital FX take time to digitize, calculate, and convert the result back to analog. If the whole signal goes through that process, you get a few ms delay, but the relative phase of the wet and dry signals is preserved.

If you use a parallel loop, then the dry signal has no delay, but the wet signal has some delay (latency). In many cases, that causes a comb filter and/or flanger-sounding artifacts that are very noticeable. Killing the dry or setting the FX unit to 100% wet can help, but some FX still have some dry signal as part of the effect.

Much of the idea that digital FX sound "digital" is based on problems that happened in the 1980s when it was new technology. Currently, most converters and FX units do very little to color the sound. A major problem when connecting them to tube amps is that tube amps are often not designed to play well with other equipment, so there are impedance mismatches that cause loss of low end, loss of high end, loss of gain, or all 3. Many FX processors are designed to be driven by a standard audio load (600 Ohms), but many tube amps have from 5k to 25k Ohm output impedances. The Triaxis and studio pre have about 6k output impedances in their loops, and the TA is 25k at the main outputs at full volume. These require FX units with at least 500k Ohm input impedances, which is not always the case, especially for line-level FX. I had to add a buffer to my studio pre FX send as a result, and it made a HUGE difference.

 

[talltxguy]

Elvis,

What kind of equipment were you using to get those impedance numbers? And what's the name of the buffer that worked for you?

Thanks,
Scott

 

[zachman]

Ando and others,

I've got an analog pedal that has a MIX function on it so that I can control the amount of effect. Do the any of the digital rack devices have a similar thing going on?

Sounds like you're saying that it does not even matter because even with say a 10% mix of effect, you're still having your signal turned to digital and back again...right?

I'm a bit concerned about having the signal go to digital and back again. Is there a spec number on the digital processors that makes the signal sound...less digital? LoL What I mean is this: does a processor with a 96 kHZ sampling rate sound less digital than one with 44.1? Or is it the digital conversion? Whether it's high end Lexicons or an Eventide H8000, the highest AD to DA conversion seems to be the same conversion I can get on a $200 Lexicon MX200 - 24-bit processing. I did notice that those high end processors do have dynamic ranges around 110 to 112 compared to 107dB of the MX200. Lexicon also advertises a 32/64 bit floating point internal audio DSP, a stat I didn't see mentioned on the Eventide merchandise.

Ando, have you thought about running 2 Triaxes at the same time? One dry and one wet? Assuming you had the $ to fund it, would that be a possibility?

The TC 2290, for example-- does NOT send the direct signal through the A/D converters, and runs at a 1 Meg sample rate. I run a multi-amp switching w/d/w rig using all of the gear you mentioned, and the w/d/w approach eliminates the concerns you have re: conversion rates anyway.

 

[zachman]

The studio pre is a series FX loop.

Whatever you believe about parallel vs. series, a major problem with parallel FX loops and digital FX is latency. Digital FX take time to digitize, calculate, and convert the result back to analog. If the whole signal goes through that process, you get a few ms delay, but the relative phase of the wet and dry signals is preserved.

If you use a parallel loop, then the dry signal has no delay, but the wet signal has some delay (latency). In many cases, that causes a comb filter and/or flanger-sounding artifacts that are very noticeable. Killing the dry or setting the FX unit to 100% wet can help, but some FX still have some dry signal as part of the effect.

Much of the idea that digital FX sound "digital" is based on problems that happened in the 1980s when it was new technology. Currently, most converters and FX units do very little to color the sound. A major problem when connecting them to tube amps is that tube amps are often not designed to play well with other equipment, so there are impedance mismatches that cause loss of low end, loss of high end, loss of gain, or all 3. Many FX processors are designed to be driven by a standard audio load (600 Ohms), but many tube amps have from 5k to 25k Ohm output impedances. The Triaxis and studio pre have about 6k output impedances in their loops, and the TA is 25k at the main outputs at full volume. These require FX units with at least 500k Ohm input impedances, which is not always the case, especially for line-level FX. I had to add a buffer to my studio pre FX send as a result, and it made a HUGE difference.

The main problem is most guys don't run the stuff you're talking about the most efficient way like they should, because it is involved and usually more expensive than they're willing/able to deal with.

Trust me when I tell you-- I have NO latency, or digital artifact issues at all, resulting from ANY of the stuff you're talking about. It doesn't have to be so mysterious and convoluted.