SP0256 Voice Generator - Revision history

MacDeath at 21:49, 19 December 2010

2010-12-19T21:49:31Z

MacDeath at 21:48, 19 December 2010

2010-12-19T21:48:03Z

Nocash: /* Sample Rate and Repeat Timings */

2010-01-16T17:38:03Z

‎Sample Rate and Repeat Timings

Nocash: /* Sample Rate and Repeat Timings */

2010-01-16T17:36:31Z

‎Sample Rate and Repeat Timings

Nocash at 11:02, 6 January 2010

2010-01-06T11:02:49Z

Nocash at 02:26, 5 January 2010

2010-01-05T02:26:26Z

Nocash at 01:58, 5 January 2010

2010-01-05T01:58:14Z

Nocash: Created page with 'Voice Generator The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so: Amplitude --> F0 --> F1 --> F2 --> F3 --> F4 -…'

2010-01-05T01:45:28Z

Created page with 'Voice Generator The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so: Amplitude --> F0 --> F1 --> F2 --> F3 --> F4 -…'

New page

Voice Generator
The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so:

Amplitude --> F0 --> F1 --> F2 --> F3 --> F4 --> F5 --> PWM --> External
Pitch/Noise B0 B1 B2 B3 B4 B5 5kHz Filter

Another important register is the Repeat counter, which indicates when the next opcode shall be executed (and which may then load new values into the above registers).

Sample Rate and Repeat Timings
The SP0256 is (usually) driven by a 3.12MHz oscillator, and it uses 7bit PWM output. So the sample rate should be 3.12MHz/128, probably further divided by two:

Sample Rate = 3.12MHz/256 = 12.1875kHz ;82.051ns per sample

Which means one sample is 82.051ns long, that value multiplied by 64 or 91 gives the following timings per repeat:

5.251ms per repeat (noise and pause), or
7.466ms per repeat (tone with pitch=91)

That (guessed/undocumented) samplerate does more or less match the specifications that say that (unwanted PWM-) noise is above 10kHz, and that wanted pitch can be up to 5kHz. And the repeat timings do more or less match the timings shown in the allophone list.

Amplitude/Pitch/Repeat
The 8bit amplitude register defines the volume in floating point form,

Amplitude = lower5bit SHL upper3bit

The pitch defines the frequency, counted in numbers of samples per period.
For pitch=91, one HIGH sample (amplitude) is output, followed by 90 zero samples (null). That pattern is repeated as many times as specified in the repeat count, for example, with repeat=3:

__ Amplitude level (+)
| | |
|________|________|________ __ Zero level PITCH

<-Pitch-> __ Amplitude level (-)
<--------repeat=3--------->

As shown above, the generated waveform is NOT a square wave (which would have 50% high, and 50% low). After applying filters, the final waveform may look somewhat like so:

__ Amplitude level (+)
| | |
|_|_.____|_|_.____|_|_.____ __ Zero level PITCH+FILTERS
| | | | | |
| | | __ Amplitude level (-)

Note that (aside from noise) the AL2 ROM uses only one pitch value: 5Bh aka 91 decimal (meaning that all vowels are using the same base frequency, and they differ only by using different filter settings).

Amplitude/Noise/Repeat
Noise is activated when setting pitch=0. The timings are then same as when pitch=64, but instead of outputting HIGH and NULL levels, the hardware does now randomly output HIGH or LOW levels, for example, pitch=0 and repeat=5:

__ Amplitude level (+)
||| || | | | || | || ||| |
|||_|| |__|_|__||_|___|| |||_| __ Zero level NOISE
| | || | || | ||| | |
<-64->| || | || | ||| | | __ Amplitude level (-)
<----------repeat=5---------->

The exact random algorithm is unknown (probably some shift/xor stuff?), the random levels seem to be output on each sample (not only on the first sample of a repeat). Like normal pitch, the noise is passed to the 6 filters.

Pause/Repeat
The pause command sets amplitude=0. The timings are then same as when pitch=64, but the output is always NULL, for example, pause and repeat=5:

__ Amplitude level (+)

______________________________ __ Zero level PAUSE (SILENCE)

<-64-> __ Amplitude level (-)
<----------repeat=5---------->

Pause does reset the filters to 0, so the silence is not affected by filters.

Digital Filters
As shown above, the amplitude/pitch/noise output is passed through six digital filter stages (using the F0..F5 and B0..B5 registers), each stage looks like so:

_____ _____
------------------>| |------------------->| |-----+----->
_____ | SUB | ______ | SUB | |
+--->| *B |--->|_____| +--->| *2*F |-->|_____| |
| |_____| _____ | |______| _____ |
+---------------|OLDER|<---+---------------| OLD |<----+
|_____| |_____|

Ie. the incoming samples are adjusted like so:

for i=0 to 5 ;filter number
sample = sample - quant_table[F.i] * OLD.i * 2 ;F0..F5 registers
sample = sample - quant_table[B.i] * OLDER.i ;B0..B5 registers
OLDER.i = OLD.i
OLD.i = sample
next i

Whereas, quant_table is a non-linear translation table that translates the signed 8bit registers to signed 10bit factors (with 9bit fractional part, ie. 511 means 0.99), with following entries:

0 ,9 ,17 ,25 ,33 ,41 ,49 ,57 ,65 ,73 ,81 ,89 ,97 ,105,113,121
129,137,145,153,161,169,177,185,193,201,209,217,225,233,241,249
257,265,273,281,289,297,301,305,309,313,317,321,325,329,333,337
341,345,349,353,357,361,365,369,373,377,381,385,389,393,397,401
405,409,413,417,421,425,427,429,431,433,435,437,439,441,443,445
447,449,451,453,455,457,459,461,463,465,467,469,471,473,475,477
479,481,482,483,484,485,486,487,488,489,490,491,492,493,494,495
496,497,498,499,500,501,502,503,504,505,506,507,508,509,510,511

Above shows only positive values for index 0..127. Values for index -1..-128 should be 0..-511, or maybe -9..-512.

← Older revision		Revision as of 21:49, 19 December 2010
Line 107:		Line 107:

	Above shows only positive values for index 0..127. Values for index -1..-128 should be 0..-511, or maybe -9..-512.		Above shows only positive values for index 0..127. Values for index -1..-128 should be 0..-511, or maybe -9..-512.
		+	[[Category:Music and sound]]

@@ Line 4: / Line 4: @@
 * [[SP0256 Allophones]]
 * [[SP0256 Pin-Outs]]
 == Voice Generator ==

@@ Line 22: / Line 22: @@
 .4ms per repeat (noise and pause), or
 .1ms per repeat (tone with pitch=91)
 == Amplitude/Pitch/Repeat ==

@@ Line 14: / Line 14: @@
 == Sample Rate and Repeat Timings ==
-The SP0256 is (usually) driven by a 3.12MHz oscillator, and it uses 7bit PWM output. So the sample rate should be 3.12MHz/128, probably further divided by two:
+The SP0256 is (usually) driven by a 3.12MHz oscillator, and it uses 7bit PWM output, which is clocked at 3.12MHz/2, to obtain a 10kHz sample rate, the chip issues some dummy steps with constant LOW level additionally to the 128 steps needed for 7bit PWM, making it a total number of 156 steps per sample.
-   Sample Rate = 3.12MHz/256 = 12.1875kHz   ;82.051ns per sample
+   Sample Rate = 3.12MHz/2/156 = 10.0kHz   ;100us per sample
-Which means one sample is 82.051ns long, that value multiplied by 64 or 91 gives the following timings per repeat:
+Which means one sample is 100us long, that value multiplied by 64 or 91 gives the following timings per repeat:
-.251ms per repeat (noise and pause), or
+.4ms per repeat (noise and pause), or
-.466ms per repeat (tone with pitch=91)
+.1ms per repeat (tone with pitch=91)
-−
-That (guessed/undocumented) samplerate does more or less match the specifications that say that (unwanted PWM-) noise is above 10kHz, and that wanted pitch can be up to 5kHz. And the repeat timings do more or less match the timings shown in the allophone list.
 == Amplitude/Pitch/Repeat ==

← Older revision		Revision as of 01:58, 5 January 2010
Line 1:		Line 1:
		+	* [[SP0256]]
		+	* [[SP0256 Voice Generator]]
		+	* [[SP0256 Instruction Set]]
		+	* [[SP0256 Allophones]]
		+	* [[SP0256 Pin-Outs]]
		+
	Voice Generator		Voice Generator
	The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so:		The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so:

@@ Line 5: / Line 5: @@
 * [[SP0256 Pin-Outs]]
-Voice Generator
+== Voice Generator ==
 The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so:
@@ Line 13: / Line 13: @@
 Another important register is the Repeat counter, which indicates when the next opcode shall be executed (and which may then load new values into the above registers).
-Sample Rate and Repeat Timings
+== Sample Rate and Repeat Timings ==
 The SP0256 is (usually) driven by a 3.12MHz oscillator, and it uses 7bit PWM output. So the sample rate should be 3.12MHz/128, probably further divided by two:
@@ Line 25: / Line 25: @@
 That (guessed/undocumented) samplerate does more or less match the specifications that say that (unwanted PWM-) noise is above 10kHz, and that wanted pitch can be up to 5kHz. And the repeat timings do more or less match the timings shown in the allophone list.
-Amplitude/Pitch/Repeat
+== Amplitude/Pitch/Repeat ==
 The 8bit amplitude register defines the volume in floating point form,
@@ Line 50: / Line 50: @@
 Note that (aside from noise) the AL2 ROM uses only one pitch value: 5Bh aka 91 decimal (meaning that all vowels are using the same base frequency, and they differ only by using different filter settings).
-Amplitude/Noise/Repeat
+== Amplitude/Noise/Repeat ==
 Noise is activated when setting pitch=0. The timings are then same as when pitch=64, but instead of outputting HIGH and NULL levels, the hardware does now randomly output HIGH or LOW levels, for example, pitch=0 and repeat=5:
@@ Line 62: / Line 62: @@
 The exact random algorithm is unknown (probably some shift/xor stuff?), the random levels seem to be output on each sample (not only on the first sample of a repeat). Like normal pitch, the noise is passed to the 6 filters.
-Pause/Repeat
+== Pause/Repeat ==
 The pause command sets amplitude=0. The timings are then same as when pitch=64, but the output is always NULL, for example, pause and repeat=5:
@@ Line 74: / Line 74: @@
 Pause does reset the filters to 0, so the silence is not affected by filters.
-Digital Filters
+== Digital Filters ==
 As shown above, the amplitude/pitch/noise output is passed through six digital filter stages (using the F0..F5 and B0..B5 registers), each stage looks like so:

@@ Line 36: / Line 36: @@
    |        |        |
    |________|________|________     __ Zero level             PITCH
-−
    <-Pitch->                       __ Amplitude level (-)
    <--------repeat=3--------->
@@ Line 66: / Line 66: @@
                                    __ Amplitude level (+)
-−
    ______________________________  __ Zero level             PAUSE (SILENCE)
-−
    <-64->                          __ Amplitude level (-)
    <----------repeat=5---------->