Unfortunately this is just not true..carlsson wrote:Most known sound chips will produce a sound relative to frequency. A low value gives a low frequency, a high value gives a high frequency.
The AY pitch value is the opposite. Low pitch values correspond to higher frequencies and high pitch values correspond to lower frequencies. In fact in my experience of most Sound chips (SID, AY, SN76489(BBC)) operate like this.
This is due to the mechanics in producing the sound in the first place.
The basis of all sound generation for these chips is taken from the input clock frequency. The internal curcuitry divides down the clock using counters so that the lower counter values will timeout more often and invert the output. The counter is like the 6522 timers. They always run at the clock frequency but are programmable to the number of counts.
A good example is with the AY when compared to the Spectrum 128 and Atari ST. The Spectrum drives the AY with a clock frequency of half the cpu speed which equates to around 1.7Mhz. The Atari drives it with a 2Mhz clock. Because of this any music expected to run on both machines must be tuned differently (using two very different note tables). Furthermore the Hardware envelope periods will also be different.
Anyway, back to your 'article'..
Hmm, i partly agree except if you hear the sid tunes i did some years ago (these are the same C64 code running on an Oric with the SID output translated into AY pitches) sound pretty much the same in pitch resolution as the C64 original.carlsson wrote: As we have seen, the delta frequency between two octaves are fewer Hz the higher note we want to play. It will be reflected in the sound chip as each value will yield an increasingly higher frequency. We get poor note resolution at the upper end, music sounds detuned. The bigger range of possible values, the better resolution. For example the SID chip uses 16-bit values which gives it quite good note resolution.
Moving down a lot further..
It does explain what you meant but i don't see what bearing it has to the real world. Most sound chips have log pitch because of the mechanism explained above. Unless i have got it wrong (which i have many times) and the majority of sound chips are based on a well tempered scale.carlsson wrote:I hope this lengthy message explains what I meant. All of this is theoretical and has no real point in the discussion. I just wanted to point out that poor note resolution in the upper octaves is not unexpected, given on what premises the sound chips actually produce sounds.
Admittedly a bigger resolution of pitches does give the possibility of higher notes being better represented, but i have not really noticed this.
The Orics AY is capable of producing frequencies from 15.26Hz to 62.5Khz (Refer AUG Page 47). If wikipedia is to be relied on The human ear is limited to a range between 20Hz and 20Khz so the Oric is more than capable to satisfy this range.
In fact our very own beloved Oric Atmos (black one) manual says on page 106 that pitch values below 5 attract Dogs!!
Interestingly the world famous SID chip is actually only capable of producing a fraction of the Oric AY's frequency range. The SIDs range (source from wikipedia) is from 16 to 4000 Hz.
However going back to your article i do agree that a smaller range of values between semitones is not such a hindrence as thought. Even limited to 3 or 4 values between, a pitchbend may still sound smooth when swept across a long range. However Vibrato is best based on this interpolation of semitones rather than the conventional direct modification of the pitch. However Wave does not do this because if it did it would slow the process too much.
Thinking about it, it is possible to optimise the interpolation for speed by using a precision table of 4 or 8 points between semitones (using your 256 byte idea) but since the AY pitch is 12 bit thats 512 Bytes which i do not posess in the current version of wave to spare
Anyway even computing the figures is not too cpu intensive and does permit the resolution to be set within the music.
However an interesting article Carlsson, one that has stimulated my thoughts, thanks.