VOCODER version 1.0

 

This is a software based vocoder. Audio˙samples are loaded into the A and B˙inputs and a third sample is produced ˙(OUT) as a result of the two input˙samples. Unlike hardware vocoders, many˙parameters are adjustable.

 

The window in the center of the display˙is used to plot the results of each

filter band form the B channel. Along˙the bottom is a grey knob. Set this to˙the lowest point

in the spectrum range that you want to˙affect. Along the top is a similar

control which sets the highest point in˙the spectrum range. The area

between these two settings will be˙affected. The scale along the bottom is

marked in octaves relative to the sample˙frequency.

 

To the left of the FORMAT DISPLAY window˙are two faders which set the

intervals between bands. One sets the˙number of semi-tones and the other

sets Cents ( 100 cents to a semi-tone).˙Below these faders are two controls:

GROUP and SINGLE.  These are the˙controls which start the actual˙processing. Selecting GROUP, will cause˙a series of bands to be generated and˙placed in the output (OUT) sound buffer.˙Only the area between the selected HI˙and LOW will be processed. The number of˙bands generated is determined by

the interval setting. [ i.e. if the˙selected range is two octaves, and

the interval is set to 0 semi-tomes and˙50 cents, then 24 bands will be˙generated.]

 

Samples are loaded to either the A or B˙inputs. Selecting the A or B input

"circles" on the panel will cause those˙samples to be played. Selecting

the OUT circle, will play the output˙sample that is produced as a 

result of the processing. [ Below the˙OUT circle is a control marked LOOP.

If loop is turned on, the output sample˙will keep repeating after OUT is

selected. This is useful for monitoring˙the progress of the processing,

as a complex setup may take a long time˙to process. ]

 

The panel shows a block diagram of the˙architecture of the vocder. Some of 

the blocks contain numbers. To change˙any of these settings, select the

number with the cursor, and then use the˙COARSE and FINE controls (located

mid screen on the right side) to adjust˙the setting. Below the COARSE and FINE

controls are a control for the sample˙frequency and a control for scaling

the output volume of the OUT sample.

[The setting for the sample frequency

only takes effect after A, B, or OUT are˙selected. ]

 

Each of the two inputs ( A and B ) go˙into a gain control. Each is followed

be a bandpass filter. The control on the˙bandpass filter sets the resonance

( Q ) of the filter. The input gain˙interacts with the resonance setting

in such a way that; high gain requires a˙low resonance setting to avoid

clipping in the filter. The B channel˙bandpass filter is then rectified

and is sent to a lowpass filter. The˙lowpass filter has a TRACKING

control, which when turned on, causes˙its cut-off point to be adjusted

according to frequency position of the˙band being processed. The output

of this lowpass filter is then sent to a˙multiplier.  The A channel bandpass

filter is sent directly to the˙multiplier. The output of the multiplier

is then accumulated in the OUT buffer.

 

There are two routing switches on the˙panel. These switches allow several

variations in the routing and processing˙of bands. The switch that is 

next to the OUT circle is used to route˙the B channel directly to the

output without involving the A channel.˙This mode is useful for

simple filtering of the B channel and˙requires less processing time.

The other routing switch is used to˙bypass the output of the A channel

bandpass filter, and instead feeds a˙sine wave oscillator directly

to the multiplier. The sine wave˙oscillator has a control to shift the

oscillator frequency up of down in˙octaves. The initial frequency of

this sine wave oscillator is set to band˙frequency. There is a control

leading into the sine wave oscillator˙which allows the oscillators frequency

to be shifted up or down by eight˙semi-tones [ a setting of 800 provides

no shift, 900 shifts it up one semitone,˙700 shifts it down one semitone, etc..]

 

Above the OUT circle, is a control˙marked ++. When turned on, this causes

the bandpass filter to become narrower.˙This also results in slower processing

time.

 

In the extreme upper left of the˙display, along the top of the of the

interval selector, are two unmarked˙indicators. When processing begins, a

short horizontal line appears. This˙indicates that a sample is being˙processed.

When the processing is finished, it will˙disappear. If during the processing,

clipping occurs due to an overload in a˙filter, a small broken line will

appear directly below the 'in progress'˙line. It will not go away when the

processing is complete. It tells you˙that there is distortion in the˙resulting sample and that you should˙lower the gain to one of the filters.

 

The output scale control (under the˙sample rate control) is used to set the

output level of the resulting sample.˙Internally, the sample is accumulated

in a 16 bit wide buffer. It is˙transferred to an 8 bit wide buffer for

listening and saving, using this scale˙control. A single click to the right

or left of the knob will scale it up or˙down. It may take a few seconds for

the result to take affect.

 

The following are the menu controls:

 

 CLEAR  - clears the output buffers

 

 CLEAN  - cleans the display window˙without affecting the output sample

 

 LOAD A - loads the A buffer

 

 LOAD B - loads the B buffer

 

 SAVE OUT - saves the OUT buffer to disk˙as an SXV8 IFF file

 

 LOAD PRESET - loads a preset˙configuration from disk

 

 SAVE PRESET - saves a preset˙configuration to disk

 

 ABORT - suspends processing but leaves˙the buffers intact

 

 NUKE  - suspends processing, clears the˙output buffer, and cleans the display

 

 QUIT  - exits the program

 

 

 

FFT Version 1.0
 
A audio digitizer (Perfect Sound or˙compatible) must be connected 
to the parallel port of the Amiga.
 
The menu bar contains two selections:˙Parameters and Quit.
 
When Parameters is selected, a window˙opens which contains two controls:
 
The frequency control sets the sample˙rate. A faster sample rate will
provide a greater range of spectral˙analysis. A slower sample rate
will show more detail at the low˙frequency end of the spectrum. If the
audio signal has spectral components˙beyond the sample rate, they will
be reflected back across the spectrum.˙Ideally, a low pass filter would be
used to prevent any component above 1/2˙the sample frequency from getting
to the digitizer.
 
The peak meter control provides a˙"memory" for the display. Peaks are held
and allowed to decay according to the˙setting of this control.
 
The window may be closed to remove these˙two controls.
 
 
 
The display shows frequency in a linear˙format.
 
The six function keys:  F3, F4, F5, F6,˙F7, and F8 are used to select
resolution of the transform.  F3 shows 7˙bands.  F8 shows 255 bands. Etc..