On Sun, Mar 22, 2015 at 10:43 AM, Jonathan Wilkes via Pd-list <pd-list@lists.iem.at> wrote:
> On 03/20/2015 12:57 PM, Reed Perkins wrote:
>
> Hello all,
>
> [line~], [vline~], and [phasor~] are used to generate line ramps in basic
> sample-playback patches. The output of these objects is usually multiplied
> by the total number of samples in a sound file (that has already been loaded
> into an array or table) and fed into the input of something like
> [tabread4~]. In other words, we use these line-ramp objects to traverse the
> indices of a table where a sample is loaded at a given speed.
>
> My questions are these:
>
> 1. Do these line-ramps generate enough numbers such that every sample in a
> table will be read?
>
>
> No.  (And I assume you are wanting the values of the table to be output one
> after the other, in sequence, when you output them as a signal.)
>
> The determining factors for how table values are output: a) ramp duration
> (in time units), b) ramp height (end value - start value), c) the sample
> rate, and d) whether the object doing the reading is interpolating the index
> values.
>
> The sample rate in Pd is fixed, so you are only guaranteed to read every
> table value when the ratio of ramp height/duration matches the sample rate
> ratio.  If you wanted something like [line~] and [tabread~] to guarantee
> that every sample of the table is read/output/whatever, you'd need a system
> in which the sample rate changes based on the size of the array being read.
>
>
> 2. Does it matter if, say for example, [tabread4~] receives a decimal number
> for an index, like 333987.8, which can be caused by multiplying the output
> of [phasor~] (which goes from 0-1) by the total amount of samples (usually a
> much larger number).
>
>
> Yes, because [tabread4~] does interpolation.  The [tabread~] object does no
> interpolation so the number after the decimal point in your index wouldn't
> make any difference.
>
> For example:
>
> [0 44099 2000(
> |
> [line~]
> |
> [tabread~ array1] <-- a table of size 44,100
>
> This will output every value of your table twice in a row, because your
> taking twice as long to read the entire table.  However, that's probably not
> what you want, and if you listen to that results vs. [tabread4~], you'll
> hear why interpolation is a good thing in this case.
>
>
> 3. Does the output of [line~] and [vline~] vary due to being asked to
> generate a ramp faster or slower? If I ask [line~] to go from 0-555987 in
> 3789 milliseconds, will the actual output be the same or different if I then
> ask [line~] to go from 0-9876545 in 40 milliseconds
>
>
> I'm not sure what you're asking.  Are you asking whether the samples output
> from 0-555987 will be the same in both cases?  If so, the answer is no.  The
> [line~] object is outputting floating point numbers in the range you
> specify, over the duration you specify, aligned to block boundaries.
>
>
> I realize this is totally theoretical, because in all honestly I wouldn't be
> able to hear a difference if samples are being skipped, but I want to know
> :)
>
>
> But you do.  If the sample rate is 44,100 samples per second, and you read
> from 0 to 44,099 in one second with [tabread~] you'll hear all the samples
> being output.  But if you read from 0 to 44,099 in _half_ of a second you'll
> be skipping every other sample.  You'll certainly perceive the difference as
> the sound recording going _twice_ as fast.
>
> Essentially, the [tabread4~] object is for those situations where you know
> you'll be playing back at a ramp height/duration ratio that doesn't match
> the sample rate ratio.  Or where you'll often be speeding up or slowing
> down.
>
> -Jonathan
>
>
> Thanks for your time.
>
>
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