Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.
Download on the App StoreAudiobus is the app that makes the rest of your setup better.
SOLVING CPU CRACKLE!
This is probably obvious to most of you, but it wasn't to me. I thought the crackling noise from CPU overload was something I had to get rid of. I struggled and did a pretty good job, but it took time and directed my choice of apps. Admittedly one gb of RAM on my iPad4 doesn't help and I plan to upgrade to at least two if not four gigs. What I didn't realize was that the CPU overload and crackling does not affect the mixdown! With my last project I stumbled on this... don't quite remember the "aha" moment, but all of a sudden I was just accepting the crackles and mixing down pure tracks. It was a stunner! Obviously no good for live playing and it is not a pleasant aural experience, but knowing something good lies at the end of the road makes it endurable.
Of course there are limits to the crackle decibel level. I still can't use most of SM1 s presets. Those will have to wait till I step up to a Pro in October, or at least the 2 gb 2018 iPad. Am I missing something here? Or did nobody mention this because it is so obvious?
Comments
We all hear crackling and tend to do something to stop it:
Change to larger buffer sizes (giving up latency on the keyboard/PADs)
Choose another AU App to lower CPU usage
Turn off some FX
Kill an App in AB3 or AUM or ... Your-favorite-AU-host
Write to this Forum for clues or workarounds
When you freeze a MIDI track of a virtual instrument the CPU is only tasked with that ONE job so it often does it without adding any unwanted noise because it can focus and take as much time as needed to create this new sequence of numbers in a wave file.
It's moments like these that help us all learn... thanks for playing the IOS game and making us all a lot smarter in the process. Now this important detail is documented for future players just learning the game rules.
Here's where the crackling comes from - the audio output hardware has a buffer that must constantly be filled with new numbers to make a continuous sound on the Right + Left Channels. If the CPU misses the deadline to add more numbers to the buffer there's a sudden change from the last number to zero. This is many cases is like a musical instant jump telling the speakers to travel 8 milimeters or so in 0.0 seconds. It can't but it tries and makes a clicking noise in the instant jump sometimes literally running the sound transducer into the end of it's travel.
Steady smooth numbers in the buffer makes for a great sound...
instant jumps in number values makes a crackle and the same non-zero number for too long burns out the speaker coils... the numbers are asking it to hold in one place producing no more sound (not moving any air) and the electricity running into this static speaker coil makes the wires get hot fast and smoke results. This also happens when you top out the numeric range and enter into the "clipping" of the signal. "Just stay at the end of your excursion path speaker for 3 milliseconds and get hot. No sound... just heat.
Remember the perfect sign wave and how smooth it looks. That's a great signal for a mechanical swing... a lovely alignment of input "driver" numbers and the physical equipment which acts like a sound wave trampoline.
Rendering trampoline instructions (MIDI to Audio) is a number crunching exercise. So actual sound waves happen until those instructions (a wave file) are sent to the trampoline (your headphones).
I like a good analogy to explain complex details. I also hope it doesn't appear like I'm talking down to anyone. Just trying to raise the level of understanding about the physics and electronics of IOS sound making.
So, how big do you think that output buffer for audio is? How many sequential numbers at 44.1Khz? How long before it goes empty? Google it. I don't have a clue. Probably just a couple milliseconds so the latency between a keypress and us hearing sound is "instantaneous".
TL;DR "You never asked the right question before." You're not the first to miss this detail and discover the answer using the scientific method. And not the last.
It wasn't for me and I'm very surprised reading this !...
Thanks for the physics lesson @McDtracy. You would be that physics teacher that peppers his students with dry wit as to the harshness of real life and the laws of physics as applied to stumbling on your way to the bathroom in the dark and hitting your head on the sink. Kind of like the Keystone Kop of gravity.
Did I miss something or did you not explain why a mixdown presents no such problem? Obviously the numbers are all calmly sitting in a waiting room talking about 1s and 0s, talking about themselves (ego is not limited to us humans) and how a 1 doesn't buy a gallon of gas anymore abd how he zeros can never get a date, but why is the pressure off? Is the buffer changed in mixing?
And also, how do you change the buffer? I don't always see it in the settings.
The crackles issue is related to realtime performance. An audio apP in realtime has to perform all the calculations required to keep audio running smoothly in real time or else there will be crackles. If there is too much competition for the CPU, it might not get all the calculations done in time.
When you freeze a track, an app can take however much time it needs. If there is a momentary glitch in CPU availability, the calculations continue from where they left off.
Think of it as you trying to do sums in your head as someone calls out numbers vs having a column of the same numbers written down on paper that you can solve in your own time.
Do you hear any sound when performing a mixdown? No so it's just a CPU job and can run really fast on the iPad Pro or slower on your iPad 4 and still calculate the same perfect mixes.
When you are hearing sound then this whole complex factory of calculating sounds and adding them together is running against time and with too much stuff going on you can experience dropped buffer refreshes.
There are 2 references to buffers:
1. Application Buffering
2. iPad Hardware Audio Buffers
Setting better Application buffering to delay crackling:
Go to the Setup -> "Audio" Page
There's a on/off button labeled "Large Recording Buffer". Turn that "ON" (Blue Glow) if you're hearing crackling. If not it doesn't have to be ON but I suspect you'll need this ON with great sounding AUv3 Apps in Cubasis.
and set a Latency Choice:
1. Medium
2. Low
3. Ultra-Low
Medium gives the application more time to do the most urgent tasks but also shows up in response to your playing. Try it and if it ruins the illusion of a real piano then start with Low. It that's no good try Ultra-Low with Large Recording Buffer and see what you can do before Crackling starts. If it does... back-off on Latency.
NOW, Buffer #2 is built into the iPad hardware chipset. You can't change it but if the CPU doesn't give this buffer enough data because it's too busy you will hear "crackling" as the Analog-to-Digital Converter uses garbage or old data that might create one of those huge changes in values rather than a smooth audio signal. You can take the pressure off this hardware buffer by using the slowest bit-rate 44.1Khz and 16-bit audio.
The Application buffering is designed to allow the CPU to copy larger blocks of sound less often. Smaller buffers tighten up the time intervals between CPU audio moves between application and hardware buffers.
The ideal live situation is generating all the sound and FX without ever missing the hardware buffer updates. We can configure so many sounds and FX'es and input so many notes from the MIDI controller and effectively "break" the system's ability to get all it's work done. Then we get crackling output from the A-D converters in our ears.
Well that was interesting.
How about reducing polyphony?
There's a good point to make here: the rate that notes requiring conversion to sound is important. Have you ever pulled off a really nice piano run of fast notes and heard about 2/3's of them in the output?
Some software will protect it you from crackles by just throwing away notes and reducing the CPU load at that time.
You can insist on it throwing away more simultaneous notes but changing this "polyphony" setting to a smaller number. Remember the sustain pedal keeps a note "in play" until you lift the pedal so counting 10 fingers isn't the best way to determine the number of notes you'd like to max out with.
Also we often drive our synths with MIDI input streams that can generate a lot of notes: both fast and in heavy layers.
If the notes stream is thick you might not notice dropped notes but if one of those notes is your critical melodic theme, you should hear something is broken.
Many synth's also offer a high-resolution setting which is typically a bit-rate (16 vs 24) setting for the sound calculating.
A piece of software that never produces crackles would likely introduce extra copies of the most recent buffer(s) if a newly calculated buffer is not ready in time. You have probably heard this type of effect on the early Internet Phone apps. You'd hear a single word elongated like the person was a robot breaking into song. No crackling but a new type of musical noise. One that some auto-tune settings make persistent.
HERE'S A THOUGHT QUESTION: If we double the iPad RAM from 2GB to 4GB doesn't the CPU have twice the work to do and crackle more often? Don't we have to double the CPU clock rate when we double the RAM? What do you think?
Not at all. Think of RAM as "super fast storage space". Both data and code can be loaded into RAM. RAM limitations generally slow things down because the OS needs to have critical data and instructions in RAM to execute them. When you have limited RAM, the OS sometimes has to dump things from RAM and then reload them when they are needed -- which slows things down. When you have more RAM, the OS can load more instructions and data (like audio samples) and have them were the OS can access them superfast. The more apps you have running, the more they are competing for that superfast but limited RAM.
So, more RAM means your device works less hard not more hard (unless apps are really badly designed).
There are certainly cases where more RAM doesn't help but it would be extremely unlikely to ever hurt.
That sounds like a very good tactic- have a Plan B the software can switch to, when it becomes obvious the cpu can't complete the work to render the audio, in a given buffer period, rather than throwing up its hands and saying, "I give up!". This would make sound quality a little degraded/less accurate, but nowhere near as bad as loud cackles and pops.
This is valuable information for a lot of us! Keep going. I want to reread the whole thread.
If cracklings was my only problem I would bow down to any crackpot, but unfortunately it’s worse....
My 2017 iPad Pro freezes all the time, especially when writing in the forum. So I ask yall now... if you have lesser iPads, they must freeze too, if it’s the websites fault. Anyone experiencing freezing when writing in here?
No, It didn’t help put in a sweater. :-(
Which browser are you using? Apple's Safari?
If Yes.
Download another browser like Google Chrome to test. It may have better behavior on the Forum Website.
How frustrating it must be. Now @LinearLineman won't get an iPad Pro.
If the hangup is pretty predictable I'd go to the Apple Store and be irritated in front of new customers. Sometimes they swap it out to show they care. Apple Cares.
As a rule of thumb RAM has barely any impact on the processing/calculation/synthesis power of apps. For synth apps, CPU and cache speed will have a lot more to say about crackling than your available RAM will.
For sample-heavy audio players RAM may have a bit more impact, but even then the CPU will determine how much you can time-stretch or interpolate or filter before you'll get crackling.
LoL yeah man, it’s Safari. The nearest Apple Store I believe is in Stockholm Sweden, so that’s out of the question.
I think I’ll take it to the place I bought it and take it on warranty. It happened to my 2015 Pro also, until it just went dead black. I got a new one.
Yeah, when I updated it took over 3 minutes to reboot. Usually it takes 20 secs.
The next reboot took 90 secs, then a minute... it kept chopping off reboot time until it was back at 20.
I felt immediately something was wrong when I had updated.
Maybe a fresh reinstall will be healthy... perhaps via iTunes on my Mac.
I feel your pain. I'm sure you'd rather be making music.
This is just way too much thinking.
I only get crackling from a handful of apps.
I really just need those couple apps to have the developers fix the performance issue.
I am more concerned with the size of the apps these days.
Quite true. The OP pushes his older iPad to render symphonies using the best acoutics sounding products available (BeatHawk, iFretless, iSymphonic and many others).
So, his thought is "why don't these companies just fix the problem for me" and the problem is apple makes a gun and Apps are the bullets. We still need to learn how to aim and use the gun properly. (I hope that doesn't sound insulting) but we have all shot ourselves in the foot with new features by loading up 10 AUM channels with Apps and FX'es and hearing something decidedly "non-musical". There are limits... find them and then back off a bit.
Adding more RAM (which for iPad's and iPhones is a buying criteria and not an upgrade) seems to let you run more apps before you hit the non-musical zone.
I know the OP is considering an iPad Pro purchase to get that 4GB of RAM and hopefully have more stability making "Synthonies".
I would like some names of apps.
Because I have a new iPad and MODEL 15 / MODEL D still cause issues quick into use many times.
@McDtracy, not quite sure you are reading me correctly. My original statement for this thread was merely that crackling disappears when I mix down so I put up with crackling. I just thought it valuable that novices know this. I thought more RAM would help with crackling and was looking forward to a diminishment of the noise but @brambos has straightened me out on that. I assume a new iPad of any class will have a lot more CPU power than my ipad4. So perhaps that will reduce the crackling issue.
i have done most of the things mentioned to avoid crackling, correct buffer setting on Cubasis, freezing tracks when it will allow me, closing unused apps. My instrument load is never above four tracks and I still have crackling sometimes. Probably I will just get a 2018 iPad 128 gb and be happy with any improvement I get. Still, I understand things a lot better from the posts on this thread.
The current iPad line all have much more horse power than previously. The iPad 2018 has a lot more CPU than the non-pro iPads that preceded it. This page will give you a sense of how the horsepower of various iOS devices compare:
https://browser.geekbench.com/ios-benchmarks
There is more to the crackle story than just raw horsepower -- but it is a lot of the story.
HUMOR_FONT ON
I did NOT read it correctly. Never mind. My head still resides permanently up my arse. "Can you hear me now?"
"What causes audio crapling?" Funny you should ask.
Audio Crapling is caused by the human attached to the iPad.
iPads when left alone do not make awful music but once purchased and registered they are often found to create volumes of pure excrement. Do you need SoundCloud examples or YouTube links?
Trust me... you don't want to hear examples and they could be yours.
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Sorry.
If anyone cares, I can continue to bloviate about:
And when I'm done... you would still have crackling that I really didn't explain. But you would understand "It depends on so many little details" because the complexity of these iPad running at 2+ GigaHz with 4 cores in parallel.
Honestly, what Apple has given us is extremely stable considering the number of Apps involved... and we are still not satisfied. Should we be?
I went to the electronics shop where I bought the iPad today, and they said they’ll have a look at it if I bring it with me next time. At least I’m glad I still have my 2015 Pro, if this one must in for repair. I’m transferring all important material over to iCloud now
@McDtracy "bloviate" incredible! I am totally oblovious to such a word! I agree, the iPad is a unique, resourceful and stable device. We take for granted what is being accomplished and ask for more, more, more. However, I am, as always, more interested in getting a good result than having an in depth understanding, tho the basics are welcome. I just want to know how to workaround the limitations.
Please hold forth on the multicore advantages, McD. Bloviate away!