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Docs revisions for PiPedal 2.0

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Robin E.R. Davies
2026-06-02 00:55:31 -04:00
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docs/ChoosingAUsbAudioAdapter.md
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@@ -11,22 +11,20 @@ The quality of the audio adapter you use dramatically affects the quality of the
Cheap USB audio adapters, claim to to support 24-bit audio, and happily provide 24 bits of data. The problem is that they are usually providing less than 16-bits of signal (the remaining bits being pure noise).
You will get decent results; but not great results. Stepping up to a more expensive USB adapter dramatically improves the quality of signal you're going to get. With a decent USB audio adapters, some of the state-of-the art Machine Learning plugin produce results that are as good as or better the Helix or Kemperer amp emulations.
You will get good results; but not astounding results. Stepping up to a more expensive USB adapter dramatically improves the quality of signal you're going to get. With a decent USB audio adapters, NAM A2 amp emulations are significantly better than Helix or Kemperer amp emulations.
I think it's worthwhile, at this point, to make a brief discursus into the state of the art when it comes to machine learning models of guitar amps. There are two major Machine Learning amp simulators that are in the public domain. Jatin Chowdhury produced some of the first really impressive Machine Learning amp simulators (I believe) as part of his PhD thesis. Jatin Chowdhury's ML amp simulation library (which was graciously provided under an open-source MIT license) forms the core of the ToobML plugin included with PiPedal. Steven Atkins' Neural Amp Modeler library (also provided under an MIT license) is the other major ML implementation, that implements a variety of Machine Learning algorithms that have been developed since Jatin Chowdhury's initial publication of his results. TooB Neural Amp Modeler uses Steven Atkins' Neural Amp Modeler library. And both have large community-developed libraries of amp models. The quality of amp simulations produced by both of these libraries is breathtaking. As I said previously, as good as or better than Helix or Kemperer amp emulations.
I personally use and recommend the both the MOTU M2, and Focusrite Scarlett 2i2 4th gen (not the Solo, or 3rd gen models which have significantly less dynamic range). There are plenty of other pro-quality audio adapters that will probably work as well. Check the specs carefully, signal-to-noise-ratio is what matters, not bits of data. (This may show up on a datasheet as Dynamic Range, as well). Cheaper USB audio adapters that sell for less than US$70 will almost certainly not provide adequate signal-to-noise ratio for best results, and invariably won't provide S/N ratio specs for very very good reasons.
But to get Helix-quality (or better) results, you need a good USB adapter. For amp simulators, particularly, every extra bit of input signal is precious.
Ideally, you want a USB adapter that provides an input volume knob, and an instrument-level input jack, and it's enormously helpful to have a VU meter to display input signal level to the device. Microphone and RCA jacks will have the wrong input impedance, which may affect your guitar tone.
I personally use and recommend the Motu M2 USB audio adapter, although there are plenty of other pro-quality audio adapters that will probably work as well. Although, the MOTU devices are -- in my experience, exceptional. Check the specs carefully, signal-to-noise-ratio is what matters, not bits of data. Cheaper USB audio adapters that sell for less than US$70 will almost certainly not provide adequate signal-to-noise ratio for best results, and invariably won't provide S/N ratio specs for very very good reasons.
For best results, you want the input signal to the DAC to be as high as possible without clipping. Digitally clipped input signals sound horrible. And every db below "as high as possible" brings up the noise floor. Which is why a VU meter on the
USB adapter is helpful. The input signal should be peaking solidly in the yellow range of the VU meter, and must NEVER go into the red range.
Ideally, you want a USB adapter that provides an input volume knob, and an instrument-level input jack, and it's enormously helpful to have a VU meter to display input signal level to the device. Line-level or RCA jacks will have the wrong input impedance, and that has strange effects when 20 feet of guitar cable and tone controls that are designed for instrument-level impedance are involved. For best results, you want the input signal to be as high as possible without clipping. Clipped input signals sound horrible. And every db below "as high as possible" brings up the noise floor. Which is why a VU meter on the
USB adapter is helpful.
We recommend "gain-staging" your input signal to -6dbFS. Input and output signals of each successive plugin in your signal chain should be adjusted so that the signal is approximately -6dBFS when you are playing loudly. This is a good general rule of thumb for getting the best possible sound out of your plugins, and is particularly important for getting the best possible sound out of NAM A2 amp models. And this rule applies to the input signal coming into PiPedal from your USB adapter as well. Gain-staging the input signal to -6dBFs provides a little bit of safe headroom to avoid hard-clippping of the input signal. If you select the Start node in your PiPedal preset, you can see
the level of the input signal level coming into PiPedal from your USB adapter on the left-side VU meter. If you prefer to use a lower input trim on your USB adapter, adjust the input trim control in the Start node so that the right-side VU meter is peaking at around -6dBFS when you are playing loudly.
If you don't have an audio adapter with a VU meter, pay close attention to the input VU meter of the first effect in your guitar effect chain. That will indicate the signal level coming into the USB adapter. Ideally, you want the value peaking solidly in the yellow range of the VU meter, and NEVER going red.
Again, the MOTU M2 excels in this regard. It provides large volume knobs for input and output trim, along with very readable VU meters on the front panel which indicate both input and output signal levels.
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[<< An Intro to Snapshots](Snapshots.md) | [Up](Documentation.md) | [Optimizing Audio Latency >>](AudioLatency.md)
[<< Neural Amp Modeler Calibration](NamCalibration.md) | [Up](Documentation.md) | [Optimizing Audio Latency >>](AudioLatency.md)