How many audio tracks can I expect in Cakewalk Pro Audio?


Theoretically, the amount of tracks in Cakewalk Pro Audio is unlimited, but the 
actual limit is determined by your PC (CPU speed) and hard drive (seek time 
and transfer rate). Another factor is the sample rate you use when 
recording/importing audio files. Sampling/recording is done at a given rate. 
This rate determines the highest frequency that can be rendered at the rate. 

The mathematical rule is: if you're sampling at a frequency of F(s), the highest 
frequency that can be rendered is F(s)/2. This should probably explain why 
you don't hear about sampling rates much higher than 48kHz, since half that 
is 24kHz, which is already more than the upper threshold of human hearing.


When audio is digitized, the data is sampled and quantized. Quantization is done 
at a given resolution, the sample depth (bits per sample). This depth 
determines the dynamic range (ie, range of loudness-to-softness) that can be 
rendered. Since each bit of resolution effectively doubles this range, you can 
see that ideal 8-bit audio gives 48dB of dynamic range (ie, 6dB/bit times 8 bits), 
while 16-bit audio gives 96dB of dynamic range. Cakewalk Pro Audio supports 
16-bit audio (2 bytes per sample), and three sampling rates: 

11kHz, 22kHz, and 44kHz (CD quality).


Let's get specific in how all of this factors in when determining the maximum 
amount of tracks you can expect from you computer:

When you multiply the sampling rate, the bits per sample, and the number of 
channels, you come up with a data rate for that audio. Let's look at the per-
channel data rates:

11kHz = 11025 samples/sec * 2 bytes/sample		= 22050 bytes/sec
22kHz = 22050 samples/sec * 2 bytes/sample		= 44100 bytes/sec
44kHz = 44100 samples/sec * 2 bytes/sample		= 88200 bytes/sec

Remember, this is all per-channel. So, for example, to play 8 channels (tracks) 
of 44kHz audio, you need a sustained data rate of 88200*8 = 705,600 bytes/sec.


All audio that is played must come off your hard disk. So if your hard disk can't 
move the data at the rate, the audio won't play smoothly. Using this fact, you 
can work backwards from your disk's transfer rate and determine the 
maximum number of tracks that can be played.


For example, using Norton SYSINFO, you determine that your hard disk has an 
average transfer rate of 1.4MB/sec. This means:

(1.4MB/sec)/(88200 bytes/sec/track) = 16 channels (tracks).

So even if you had a Cray for a CPU, the hard disk sets an absolute limit of 16 
channels (tracks).


In reality, playing back audio in Cakewalk Pro Audio is more complex than 
simply copying the data from the hard disk to the sound card/digital audio 
interface. Assume we can dedicate 20% of the CPU's resources to mixing audio. 
This is a very generous estimate, considering all the other things Cakewalk 
Pro Audio has to do during playback.
For example, on a low-end 33mhz 486, 20% equals about 6M CPU cycles per 
second. Assume it takes minimum about 16 cycles to mix a single sample of 
digital audio (another generous estimate). To mix a full second of audio at 
44kHz requires:

16*44100 = 705K cycles per channel.


Working backwards from our self-imposed limit of 20% CPU usage, we get:

(6M cycles/sec)/(705K cycles/channel) = 8.5 channels


So even with these generous performance estimates, the most you could ever 
expect from a 486 33mhz is 8 channels (tracks). 

So what does all this mean? We can come up with quick rules of thumb to 
approximate expected performance based on your hardware:

- Max channels is at most hard disk data rate (in MB/sec) times ten.
- Max channels is at most CPU speed (in MHZ) divided by four.


Note:

- SmartDrive is occasionally a good thing. In particular, if you're playing a file 
that consists of lots of the same audio played over and over, or if you've got a 
huge cache but a slow disk, then it pays off to keep caching.

- DoubleSpace and Stacker are never, ever a good thing when playing digital 
audio. Avoid them at all cost.