In the previous Friday Tip of the Week, we covered how recording soft synths and amp sims at higher sample rates (like 96 kHz) can give higher sound quality in some situations. However, we also discussed some issues involved with recording at higher sample rates that aren’t so wonderful.
So this week, it’s time for a solution. Offline upsampling to higher sample rates can let you retain the CPU efficiencies of running at a lower sample rate, while reaping the sonic benefits of recording at higher sample rates… and you can do this in Studio One by upsampling in a separate project, rendering the file, and then importing the rendered file back into your original project.
But wait—wouldn’t you lose the benefits of upsampling when you later convert the sample rate back down to 44.1 kHz? The answer is no: Rendering at the higher sample rate eliminates any foldover distortion in the audio range, sample-rate converters include an anti-alias filter to avoid this problem, and 44.1 kHz has no problem playing back sounds in the audio range.
However, note that upsampling can’t fix audio that already has aliasing distortion; upsampling audio to 96 kHz that already contains foldover distortion will simply reproduce the existing distortion. This technique applies only to audio created in the computer. Similarly, it’s unlikely that upsampling something recorded via a computer’s audio interface will yield any benefits, because the audio interface itself will have already band-limited the signal’s frequency range so there will be no harmonics that interfere with the clock frequency.
UPSAMPLING IN STUDIO ONE
We’ll assume a 44.1 kHz project sampling rate, and that the virtual instrument’s MIDI track has been finalized but you haven’t transformed it to audio yet. Here’s how to upsample virtual instruments.
That’s all there is to it. If you want to upsample an amp sim, the process is similar: export the (presumably guitar) track, save the amp sim preset, render at 96 kHz, then import the rendered file into the 44.1 kHz project.
Listen to the audio example “Upsampling with Amp Sim,” which plays the sound of an amp sim at 44.1 kHz and then after upsampling to 96 kHz. The difference isn’t as dramatic as last week’s synth example, but you’ll still hear that the upsampled version is clearer, with more presence.
Do bear in mind you may not want the difference caused by upsampling. When I did an upsampling demo at a seminar with a particular synthesizer, most people preferred the sound with the aliasing because the upsampled sound was brighter than what they expected. However when I did upsampling with an amp sim, and with a different synth, the consensus was that the upsampled version sounded much better. Regardless, the point is now you have a choice—hear the instrument the way it’s supposed to be heard to decide if you like that better, or leave it as is. After all, distortion isn’t necessarily that horrible—think of how many guitar players wouldn’t have a career without it!
Although upsampling isn’t a panacea, don’t dismiss it either. Even with synths that don’t oversample, upsampling may make no audible difference. However, sometimes synths that do oversample still benefit from upsampling; with some sounds, it can take 4x or even 8x oversampling to reproduce the sound accurately. As always, use your ears to decide which sound works best in your music.
The controversy about whether people can tell the difference on playback between audio recorded at 96 kHz that’s played back at 44.1 kHz or a higher sample rate (such as 96 kHz) has never really been resolved. However, under some circumstances, recording at a higher sample rate can give an obvious, audible improvement in sound quality. In this week’s tip we’ll investigate why this happens, and in next week’s tip, tell how to obtain the benefits of recording at a higher sample rate in Studio One with 44.1 and 48 kHz projects.
REALLY? CONVINCE ME!
A Song’s sample rate can make a difference with sounds generated “in the box,” for instance using a virtual instrument plug-in that synthesizes a sound, or distortion created by an amp simulator. Any improvement heard with high sample rates comes from eliminating foldover distortion, also known as aliasing.
Theory time: A digital system can accurately represent audio at frequencies lower than half the sampling rate (e.g., 22.05 kHz in a 44.1 kHz project). If an algorithm within a plug-in generates harmonic content above this Nyquist limit—say, at 40 kHz—then you won’t hear a 40 kHz tone, but you will hear the aliasing created when this tone “folds down” below the Nyquist limit (to 4.1 kHz, in this case). Aliasing thus appears within the audible range, but is harmonically unrelated to the original signal, and generally sounds pretty ugly.
Foldover distortion can happen with synthesized waveforms that are rich in harmonics, like pulse waves with sharp rise and fall times. (Amp sims can also be problematic; although their harmonics may be weak, if you’re applying 60 dB of gain to create overdrive or distortion, the harmonics can be strong enough to cause audible aliasing).
SO IS IT A PROBLEM, OR NOT?
Not all plug-ins will exhibit these problems, for one of four reasons:
Many modern virtual instruments and amp sims oversample, and DAWs can handle higher sample rates, so you’d think that might be the end of it. Unfortunately, there can be limitations with oversampling and higher project sample rates.
Furthermore, with plug-ins that oversample, the sound quality will be influenced by the quality of the sample-rate conversion algorithms. It’s not necessarily easy to perform high-quality sample-rate conversion: check out comparisons for various DAWs at http://src.infinitewave.ca (where, incidentally, Studio One rates as one of the best), and remember that the conversion algorithms for a plug-in might be more “relaxed” than what’s used in a DAW.
So what’s a musician to do? In next week’s Friday Tip of the Week, we’ll cover how to do upsampling in Studio One to reap the benefits of high-sample-rate recording at lower sample rates. Meanwhile, if you still need to be convinced recording at different sample rates makes a difference, check out this audio example of a synthesizer recorded in Studio One first at 44.1 kHz, and then at 96 kHz:
A Sweeter, Beefier Ampire
Let’s transform Ampire’s Crunch American from a motor scooter into a Harley. Here’s our point of departure:
Insert the Multiband Dynamics before Ampire. The default patch is fine, but drag the High Mid and High gain and ratio settings down all the way. The goal here is to add a bit of compression to give more even distortion in the mids and lower mids but also, to get rid of high frequencies that, when distorted, create harsh harmonics.
After Ampire, insert the Pro EQ. The steep notch around 8 kHz gets rid of the whistling sound you’ll really notice in the before-and-after audio example, while the high-frequency shelf adds brightness to offset the reduced high frequencies going into Ampire. But this time, we’re increasing the “good,” post-distortion high frequencies instead of the nasty pre-distortion ones.
Those two processors alone make a big difference, but let’s face it—people don’t listen to an amp with their ear a couple inches from the speaker, but in a room. So, let’s create a room and give the sound a stereo image with the Open Air convolution reverb. I’ve loaded one of my custom, synthetic IR responses; these are my go-to impulses for pretty much everything I do involving convolution reverb, and may be available in the PreSonus shop someday. Meanwhile, feel free to use your own favorite impulses.
Of course, you can take this concept a lot further with the Channel Editor if you want to tweak specific parameters to optimize the sound for your particular playing style, choice of pickups, pickup type, and the like…hmmm, seems like that might be a good topic for a future tip.
That’s it! Now all that’s left is to compare the before and after example below. Hopefully you’ll agree that the “after” is a lot more like a Harley than a motor scooter.
Create Virtual “Room Mics”
Room mics can add ambiance and enhance the stereo image, but with close-miking and direct injection recording, we lose that sense of space. The lack of room mics is particularly noticeable with an instrument recorded direct, when it’s mixed with miked acoustic or electric tracks; the direct track just won’t seem to mesh quite right with the other sounds.
Room mics add short, discrete echos. Splitting the audio into four Analog Delay processors as parallel inserts does a fine job of emulating room ambiance.
First, set up the Splitter for four splits, and choose Channel Split for the Split Mode.
Set the controls on the four delays identically except for the four time parameters; turn off Sync and choose 11, 13, 17, and 23 ms. These are prime numbers so they don’t create resonances with each other.
Now use the Channel Editor to create macro knobs for controlling the Mix, Feedback, and High Cut. Assign Knob 1 to the Mix controls on all four delays. Set this to go from minimum to maximum so that if you use this FX Chain as a bus effect, you can set Mix for maximum (no dry signal). Otherwise, when used as an Insert, you’ll likely keep the Mix at 50% or below.
The second knob controls Feedback level. I’ve limited the maximum amount to around 60% for each of the delays. Experiment with this knob depending on the audio source; more feedback gives more diffusion. With percussive instruments like drums, you’ll want more feedback than with sustained instruments.
The third knob controls the amount of High Cut for the delays. Set this so the High Cut doesn’t go much lower than 2.5 kHz.
To hear what this FX Chain can do, load a mono AudioLoop like Guitar > Pop > Dry > 01a Basement Jam E min. Set Mix and Feedback to around 40%, and High Cut to 7 kHz or so. You’ll hear the guitar playing in a room, with a lifelike stereo image.
And don’t forget to save the FX Chain—you’ll likely want to use it again!