You're surely better off using open("|..."), especially considering the problem is probably in the argument passed to echo. (quotes, new lines, other shell special characters?)

$text     = "lots of text\n" x 150;
$filename = 'FILENAME.WAV';

open(TEXT2WAVE, '|text2wave -eval "(voice_cmu_us_slt_arctic_hts)" -sca
+le 1.5 -F 8000 -o ' . $filename . ' - ')
or die("Can't execute text2wave\n");

# Autoflush TEXT2WAVE:
{ my $f = select(TEXT2WAVE); $|=1; select($f); }

print TEXT2WAVE ($text);

close(TEXT2WAVE);
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