The MarySpeech Service can be used to generate speech from text using the MaryTTS project.

1. General

It's different from most other speech services (AcapellaSpeech & GoogleSpeech) as it is OPEN SOURCE (Yay!) and doesn't even require an internet connection (Yay! x2) as everything is generated locally and offline.

The downside is that you have to pre-download the rather big voice-file(s) you want to use.

Also the quality might not be as great compared to it's competitors (e.g. Acapella & Google), but it's free and nobody can simply "shut it down".

Another cool thing about MarySpeech is that you can apply paramerized voice effects to your voice.

2. Voices

MarySpeech has many different voices you can select and use, below is a table listing all of them. There may be more voices (and languages) available, but these are the voices officially registered in MaryTTS.

All voices are available through an additional download, you can install a voice by simply calling:

maryspeech.installComponentsAcceptLicense(voicename)

and to select a different voice:

maryspeech.setVoice(voicename) or maryspeech.setLanguage(language)

• You have to install a voice before you are able to select it!
• You need to restart MRL after installing a voice!
• By installing a voice you accept it's license!
• DATE: 05.05.2017

EDIT 7/12/2018 ( Nixie voices to use )

Raw data for information

All voices together are somewhere around 5 GB.

You can build your own voice as well, but you should have at least a basic knowledge of "working with computers".

3. Voice Effects

Notation:
"Effect1(param1=value1,param2=value2)+Effect2"

Some examples thankfully provided by MaryTTS:
"FIRFilter+Robot(amount=50)"
"Robot(amount=100)+Chorus(delay1=866, amp1=0.24, delay2=300, amp2=-0.40,)"
"Robot(amount=80)+Stadium(amount=50)"
"FIRFilter(type=3,fc1=6000, fc2=10000) + Robot"
"Stadium(amount=40) + Robot(amount=87) + Whisper(amount=65)+FIRFilter(type=1,fc1=1540;)++"

(The following section is from the MaryTTS documentation.)

3.1. Volume Effect:
Scales the output volume by a fixed amount.
Parameter:
   <amount>   Definition : Amount of scaling (the output is simply multiplied by amount)
   Range      : [0.0,10.0]
Example:
amount:2.0;

3.2. Vocal Tract Linear Scaling Effect:
Creates a shortened or lengthened vocal tract effect by shifting the formants.
Parameter:
   <amount>   Definition : The amount of formant shifting
   Range      : [0.25,4.0]
   For values of <amount> less than 1.0, the formants are shifted to lower frequencies
       resulting in a longer vocal tract (i.e. a deeper voice).
   Values greater than 1.0 shift the formants to higher frequencies.
       The result is a shorter vocal tract.

Example:
amount:1.5;

3.3. F0 scaling effect for HMM voices:
All voiced f0 values are multiplied by <f0Scale> for HMM voices.
This operation effectively scales the range of f0 values.
Note that mean f0 is preserved during the operation.
Parameter:
   <f0Scale>   Definition : Scale ratio for modifying the dynamic range of the f0 contour
                If f0Scale>1.0, the range is expanded (i.e. voice with more variable pitch)
                If f0Scale<1.0, the range is compressed (i.e. more monotonic voice)
                If f0Scale=1.0 results in no changes in range
   Range      : [0.0,3.0]
Example:
f0Scale:2.0;

3.4. F0 mean shifting effect for HMM voices:
Shifts the mean F0 value by <f0Add> Hz for HMM voices.
Parameter:
   <f0Add>   Definition : F0 shift of mean value in Hz for synthesized speech output
   Range      : [-300.0,300.0]
Example:
f0Add:50.0;

3.5. Duration scaling for HMM voices:
Scales the HMM output speech duration by <durScale>.
Parameter:
   <durScale>   Definition : Duration scaling factor for synthesized speech output
   Range      : [0.1,3.0]
Example:
durScale:1.5;

3.6. Robotiser Effect:
Creates a robotic voice by setting all phases to zero.
Parameter:
   <amount>   Definition : The amount of robotic voice at the output
   Range      : [0.0,100.0]
Example:
amount:100.0;

3.7. Whisper Effect:
Creates a whispered voice by replacing the LPC residual with white noise.
Parameter:
   <amount>   Definition : The amount of whisperised voice at the output
   Range      : [0.0,100.0]
Example:
amount:100.0;

3.8. Stadium Effect:
Adds stadium effect by applying a specially designed multi-tap chorus.
Parameter:
   <amount>   Definition : The amount of stadium effect at the output
   Range      : [0.0,200.0]
Example:
amount:100.0

3.9. Multi-Tap Chorus Effect:
Adds chorus effect by summing up the original signal with delayed and amplitude scaled versions.
The parameters should consist of delay and amplitude pairs for each tap.
A variable number of taps (max 20) can be specified by simply defining more delay-amplitude pairs.
Each tap outputs a delayed and gain-scaled version of the original signal.
All tap outputs are summed up with the oiginal signal with appropriate gain normalization.
Parameters:
   <delay1>
   Definition : The amount of delay in miliseconds for tap #1
   Range      : [0,5000]
   <amp1>
   Definition : Relative amplitude of the channel gain as compared to original signal gain for tap #1
   Range      : [-5.0,5.0]
   <delay2>
   Definition : The amount of delay in miliseconds in delayed channel #2
   Range      : [0,5000]
   <amp2>
   Definition : Relative amplitude of the channel gain as compared to original signal gain for delayed channel #2
   Range      : [-5.0,5.0]
   ...
   <delayN>
   Definition : The amount of delay in miliseconds in delayed channel #N
   Range      : [0,5000]
   <ampN>
   Definition : Relative amplitude of the channel gain as compared to original signal gain for delayed channel #N
   Range      : [-5.0,5.0]
   Note: Maximum possible number of taps is N=20. Parameters for more taps will simply be neglected.
Example: (A three-tap chorus effect)
delay1:466;amp1:0.54;delay2:600;amp2:-0.10;delay3:250;amp3:0.30

3.10. FIR filtering:
Filters the input signal by an FIR filter.
Parameters:
   <type>
   Definition : Type of filter (1:Lowpass, 2:Highpass, 3:Bandpass, 4:Bandreject)
   Range      : {1,2,3,4}
   <fc>   Definition : Cutoff frequency in Hz for lowpass and highpass filters
   Range      : [0.0, fs/2.0] where fs is the sampling rate in Hz
   <fc1>   Definition : Lower frequency cutoff in Hz for bandpass and bandreject filters
   Range      : [0.0, fs/2.0] where fs is the sampling rate in Hz
   <fc2>   Definition : Higher frequency cutoff in Hz for bandpass and bandreject filters
   Range      : [0.0, fs/2.0] where fs is the sampling rate in Hz
Example: (A band-pass filter)
type:3;fc1:500.0;fc2:2000.0

3.11. Jet pilot effect:
Filters the input signal using an FIR bandpass filter.
Parameters: NONE

4. TL;DR

PRO:

• open source
• offline
• free
• different voices
• voice effects!

CON:

• not as great as paid alternatives (yet)
• rather big voice-files required

5. Further links

References :

• MaryTTS  http://mary.dfki.de/
• MaryTTS web interface  http://mary.dfki.de:59125/
• Blog post about supporting different voices http://myrobotlab.org/content/marytts-multi-language-support