Tips for Windows netbook users

It seems that quite a few forum members like to run Pianoteq on netbooks and other low-performance devices.  There’s no doubt the format is attractive... neat, portable, reasonably robust, ready access to the Pianoteq interface, not too expensive.  But many, if not all, current netbooks are less powerful than the minimum system recommended in Pianoteq’s FAQs (a CPU with dual or multiple cores, such as the Intel Core 2 Duo or AMD X2).

Some members report success with netbooks, but others are suffering audio crackles, pops and spikes, and others have compromised on piano sound quality (choosing low values of sample rate, low polyphony and so on) to avoid crackles.

I recently set up Pianoteq on a netbook and I have started using it for performances.  It took me a while to achieve a satisfactory set-up with good sound and no crackles.  It would have taken even longer without the wide range of forum posts bearing on this subject.  Thanks to everyone for posting them!

Through this post I’m hoping to contribute by bringing some of the many helpful threads together and by offering one or two new insights on getting a no-compromise sound without crackles.

Although it’s an oversimplification, I think it’s useful to think of crackles coming from two different sources: (a) processes running in the background, and (b) Pianoteq.  Both coincide with red lines on the Pianoteq audio load graph.

Generally speaking, crackles caused by processes running in the background happen even when the audio load seems to be well below 100%.  There is already an excellent guide to managing this problem: www.native-instruments.com/knowledge/questions/847 so I won’t revisit it here.

Crackles caused by Pianoteq come from the demands the software makes on the CPU for piano simulation calculations and data transfer to the sound card.  When the audio load approaches 100% the crackles occur, and of course this is most likely to happen during busy playing (lots of rapid notes plus bass notes with sustain pedal down).

What CPU performance do you need for a good Pianoteq experience – good sound with no crackles?  This is obviously an important question if, like me, you were thinking of buying a new device.

You can look up a measure of the performance of any CPU, “Passmark CPU Mark”, at www.cpubenchmark.net   Pianoteq displays a (different) CPU performance index while it runs.  Fortunately there is a correlation between the two indices, so if you know one, you can estimate the other.

Here are the Pianoteq CPU index and Passmark CPU mark for three relatively low performance systems:

Atom N280                   9       315      Several forum posts mention this CPU
Atom N2800                15       681      My new netbook (HPMini-4125sa)
Core 2 Duo 1.8GHz       20     1012      My old system,  ~= Pianoteq FAQ’s “minimum”

Some forum members have reported satisfactory performance with a Pianoteq CPU index as low as 7, although they have had to make some sacrifices on sound quality.  I have experimented with several systems and it’s my opinion that, if you do not wish to compromise on sound quality, you need a Pianoteq CPU index of 13 or more (equivalent to a PassMark CPU Mark of over 500).  With such a system you still need to be prepared to make some adjustments to the operating system and the default Pianoteq parameters, to avoid crackles.  If you don’t want to bother with such adjustments, then you need a CPU Mark of 1000 (about the same as the minimum CPU recommended by Pianoteq at www.pianoteq.com).

I’ll now try to justify my opinion by discussing several of the parameters that allow you to compromise on the piano sound quality in order to avoid crackling.

Reverb on/off
Toggling reverb off can definitely reduce crackles, although not dramatically.  I find that reverb is not really needed for public performance; in fact, I prefer to rely on the natural hall acoustic.  But reverb is useful with headphones.

Polyphony
Crackles can be reduced by reducing the Pianoteq polyphony.  The default is 48 notes.  I find 32 acceptable, but 24 sounds thin (only when the sustain pedal is down, obviously!).

Internal Sample Rate
The lower the value of the Internal Sample Rate (ISR), the fewer the calculations that Pianoteq requires the CPU to perform and the fewer data to be sent to the sound card.  So reducing ISR will reduce crackles.

The highest audio frequency that Pianoteq can produce is equal to half the ISR (the Nyquist frequency).  So if the ISR is too low, some higher frequencies will be lost.  This is not a problem with the default ISR of 44.1kHz (the same frequency as that used on commercial CDs) because the corresponding Nyquist value of 22kHz is well above the range of normal hearing.

Several forum posts recommend reducing the ISR to 32kHz (or 29.4kHz) while keeping the host sample rate at 48kHz (or 44.1 kHz).  If the ISR is 32kHz, then the Nyquist frequency is 16kHz.  It’s argued on the forum that this is still above the maximum frequency that a piano will produce (including overtones) and also that it is above the highest frequency that most people can hear.  Therefore, it’s argued, reducing ISR to 32kHz is OK.  This sounds logical, but in practice I find that with ISR= 32kHz, some notes – particularly in the mid treble – have a strange and unpleasant harshness which is not present with ISR= 48kHz.  I’ve conducted a blind test of this and listeners confirm it.

At an even lower ISR of 24kHz, the loss of high frequencies is noticeable - the piano sounds duller.

Buffer size and latency
A larger buffer size certainly helps to reduce crackles, but at the expense of latency.  Latency equals buffer size divided by host sample rate, so, latency increases with buffer size.  There is a long thread on the forum on this (search “zero latency”).  I personally find that when the latency goes above 10ms my keyboard starts to feel uncomfortably sluggish.

Host Sample Rate
Last, but certainly not least, is the Host Sample Rate (HSR), which is the sample rate at which the sound card operates.  I am using my netbook’s on-board sound card with the ASIO4ALL driver.

The HSR can be adjusted from within Pianoteq (the Pianoteq default HSR is 44.1kHz, the same as the default Internal Sample Rate).  TheBayer has reported on the forum that, surprisingly, increasing HSR reduces crackling.  TheBayer’s post does not seem to have received much response, but I can confirm his result, which is a very useful one indeed.

For example, on my netbook, I can choose HSR=48kHz, ISR=32kHz, polyphony 32 and still get crackling on busy passages.  When I change HSR to 96kHz this eliminates the crackling entirely.  And if this were not sufficient, there are two bonuses.  Firstly, the harshness in the mid-treble associated with ISR=32kHz, described above, disappears!  Secondly, the latency goes down.

To summarise, I suggest the following steps to optimise Pianoteq on a netbook:

If possible, use a CPU with a PassMark CPU Mark of over 500 (roughly equivalent to a Pianoteq CPU index of 13).
Ensure that a High Performance power plan is selected via Windows Control Panel.
Carefully disable unneeded drivers (for example network adapters) in Windows Device Manager and consider the other advice given in www.native-instruments.com/knowledge/questions/847.
Disable the background activities of anti-virus software.
Use msconfig to check the list of Windows start-up items.  I found that this contained several items pre-loaded by my netbook manufacturer.  By disabling the unwanted ones I eliminated some crackles.

Then, in Pianoteq:
Set the host sample rate to 96kHz.
Aiming for a latency of between 5 and 10ms, choose a buffer size which is a multiple of the host sample rate (I used 6 x 96 = 576).
Set polyphony to 32 notes.
Set internal sample rate to 32kHz.
Minimise the Pianoteq window (if the window is open then it uses some CPU to update the moving parts of the display - for example the velocity graph).

If crackles still occur, choose some compromises on piano sound quality that best suit your personal taste.  You can reduce polyphony, reduce sample rates, increase the buffer size, turn reverb off, reduce the number of microphones.

Hope this is helpful.  Thanks again for previous posts on this topic.